Hallo zusammen,
@Gaucho: ich hatte meine Domain gelöscht, da ich nicht sicher war, ob man die angeben soll 
Der log sieht so aus:
2019-03-29 00:38:10,101:DEBUG:certbot.main:Root logging level set at 30
2019-03-29 00:38:10,112:INFO:certbot.main:Saving debug log to /var/log/letsencrypt/letsencrypt.log
2019-03-29 00:38:10,116:DEBUG:certbot.main:certbot version: 0.10.2
2019-03-29 00:38:10,116:DEBUG:certbot.main:Arguments: [’-q’]
2019-03-29 00:38:10,120:DEBUG:certbot.main:Discovered plugins: PluginsRegistry(PluginEntryPoint#webroot,PluginEntryPoint#n$
2019-03-29 00:38:10,264:DEBUG:certbot.storage:Should renew, less than 30 days before certificate expiry 2019-03-16 15:56:1$
2019-03-29 00:38:10,264:INFO:certbot.renewal:Cert is due for renewal, auto-renewing…
2019-03-29 00:38:10,266:DEBUG:certbot.plugins.selection:Requested authenticator webroot and installer None
2019-03-29 00:38:10,267:DEBUG:certbot.plugins.selection:Single candidate plugin: * webroot
Description: Place files in webroot directory
Interfaces: IAuthenticator, IPlugin
Entry point: webroot = certbot.plugins.webroot:Authenticator
Initialized: <certbot.plugins.webroot.Authenticator object at 0x7615cfd0>
Prep: True
2019-03-29 00:38:10,271:DEBUG:certbot.plugins.selection:Selected authenticator <certbot.plugins.webroot.Authenticator obje$
2019-03-29 00:38:10,288:DEBUG:certbot.main:Picked account: <Account(8711f835251a2c941ac1395f69a4d77d)>
2019-03-29 00:38:10,293:DEBUG:root:Sending GET request to https://acme-v01.api.letsencrypt.org/directory.
2019-03-29 00:38:10,312:DEBUG:requests.packages.urllib3.connectionpool:Starting new HTTPS connection (1): acme-v01.api.let$
Interfaces: IAuthenticator, IPlugin
Entry point: webroot = certbot.plugins.webroot:Authenticator
Initialized: <certbot.plugins.webroot.Authenticator object at 0x7615cfd0>
Prep: True
2019-03-29 00:38:10,271:DEBUG:certbot.plugins.selection:Selected authenticator <certbot.plugins.webroot.Authenticator obje$
2019-03-29 00:38:10,288:DEBUG:certbot.main:Picked account: <Account(8711f835251a2c941ac1395f69a4d77d)>
2019-03-29 00:38:10,293:DEBUG:root:Sending GET request to https://acme-v01.api.letsencrypt.org/directory.
2019-03-29 00:38:10,312:DEBUG:requests.packages.urllib3.connectionpool:Starting new HTTPS connection (1): acme-v01.api.let$
2019-03-29 00:38:10,643:DEBUG:requests.packages.urllib3.connectionpool:https://acme-v01.api.letsencrypt.org:443 "GET /dire$
2019-03-29 00:38:10,646:DEBUG:acme.client:Received response:
HTTP 200
Server: nginx
Content-Type: application/json
Content-Length: 658
Replay-Nonce: CfCZZiLJfLoihRZRsITOdhx9qfZoAEhCzXSF6kFgze4
X-Frame-Options: DENY
Strict-Transport-Security: max-age=604800
Expires: Fri, 29 Mar 2019 00:38:10 GMT
Cache-Control: max-age=0, no-cache, no-store
Pragma: no-cache
Date: Fri, 29 Mar 2019 00:38:10 GMT
Connection: keep-alive
{
“9IyBRvnToJY”: “https://community.letsencrypt.org/t/adding-random-entries-to-the-directory/33417”,
“key-change”: “https://acme-v01.api.letsencrypt.org/acme/key-change”,
“meta”: {
“caaIdentities”: [
Date: Fri, 29 Mar 2019 00:38:10 GMT
Connection: keep-alive
{
“9IyBRvnToJY”: “https://community.letsencrypt.org/t/adding-random-entries-to-the-directory/33417”,
“key-change”: “https://acme-v01.api.letsencrypt.org/acme/key-change”,
“meta”: {
“caaIdentities”: [
“letsencrypt.org”
],
“terms-of-service”: “https://letsencrypt.org/documents/LE-SA-v1.2-November-15-2017.pdf”,
“website”: “https://letsencrypt.org”
},
“new-authz”: “https://acme-v01.api.letsencrypt.org/acme/new-authz”,
“new-cert”: “https://acme-v01.api.letsencrypt.org/acme/new-cert”,
“new-reg”: “https://acme-v01.api.letsencrypt.org/acme/new-reg”,
“revoke-cert”: “https://acme-v01.api.letsencrypt.org/acme/revoke-cert”
}
2019-03-29 00:38:10,648:INFO:certbot.main:Renewing an existing certificate
2019-03-29 00:38:10,649:DEBUG:root:Requesting fresh nonce
2019-03-29 00:38:10,650:DEBUG:root:Sending HEAD request to https://acme-v01.api.letsencrypt.org/acme/new-authz.
2019-03-29 00:38:10,811:DEBUG:requests.packages.urllib3.connectionpool:https://acme-v01.api.letsencrypt.org:443 "HEAD /acm$
2019-03-29 00:38:10,814:DEBUG:acme.client:Received response:
HTTP 405
Server: nginx
Content-Type: application/problem+json
Content-Length: 91
Allow: POST
Replay-Nonce: yHlBLvwksHs-fxfbkOZD12EBinqrZN3ly9yiDHVa4BY
Expires: Fri, 29 Mar 2019 00:38:10 GMT
Cache-Control: max-age=0, no-cache, no-store
Pragma: no-cache
Date: Fri, 29 Mar 2019 00:38:10 GMT
Connection: keep-alive
2019-03-29 00:38:10,814:DEBUG:acme.client:Storing nonce: yHlBLvwksHs-fxfbkOZD12EBinqrZN3ly9yiDHVa4BY
2019-03-29 00:38:10,816:DEBUG:acme.client:JWS payload:
Replay-Nonce: yHlBLvwksHs-fxfbkOZD12EBinqrZN3ly9yiDHVa4BY
Expires: Fri, 29 Mar 2019 00:38:10 GMT
Cache-Control: max-age=0, no-cache, no-store
Pragma: no-cache
Date: Fri, 29 Mar 2019 00:38:10 GMT
Connection: keep-alive
2019-03-29 00:38:10,814:DEBUG:acme.client:Storing nonce: yHlBLvwksHs-fxfbkOZD12EBinqrZN3ly9yiDHVa4BY
2019-03-29 00:38:10,816:DEBUG:acme.client:JWS payload:
{
“identifier”: {
“type”: “dns”,
“value”: “irmtraut.spdns.de”
},
“resource”: “new-authz”
}
2019-03-29 00:38:10,884:DEBUG:root:Sending POST request to https://acme-v01.api.letsencrypt.org/acme/new-authz:
{
“header”: {
“alg”: “RS256”,
“jwk”: {
“e”: “AQAB”,
“kty”: “RSA”,
“n”: "sqsXtcxkh2bEyrHRj9Ez2lkhDqAzdIOMNb99qxawB5GFvpKqnexsmrGMVzvC1I0fYcneWMhu3GpqWt0OIgG7DLDHFKV4zdKEalFQLmT3sdYZsA$
}
},
“protected”: “eyJub25jZSI6ICJ5SGxCTHZ3a3NIcy1meGZia09aRDEyRUJpbnFyWk4zbHk5eWlESFZhNEJZIn0”,
“payload”: "ewogICJpZGVudGlmaWVyIjogewogICAgInR5cGUiOiAiZG5zIiwgCiAgICAidmFsdWUiOiAiaXJtdHJhdXQuc3BkbnMuZGUiCiAgfSwgCiAg$
“signature”: "ExJs2TC5_40AGP2PNFJL5M2Vc1jYKDJO-nQMLFCZzeiHajSPvG_8H14WRYcnJi_7x4OwJ_Ri4FY-vn5TGaZR0RfRnbRIcB2dd2Xt5G5top$
}
2019-03-29 00:38:11,143:DEBUG:requests.packages.urllib3.connectionpool:https://acme-v01.api.letsencrypt.org:443 "POST /acm$
2019-03-29 00:38:11,146:DEBUG:acme.client:Received response:
HTTP 201
Server: nginx
Content-Type: application/json
Content-Length: 999
Boulder-Requester: 47794666
Link: https://acme-v01.api.letsencrypt.org/acme/new-cert;rel=“next”
Location: https://acme-v01.api.letsencrypt.org/acme/authz/VhTeLQ81UQ7d49uM7KxpCeSxchHYPzxnKt6a6Yc_xJc
Replay-Nonce: 4DDM8d7dcV8Gyu_V_cv22Mo5oZ38X94kEzrbqxcq8iY
X-Frame-Options: DENY
Strict-Transport-Security: max-age=604800
Expires: Fri, 29 Mar 2019 00:38:11 GMT
Cache-Control: max-age=0, no-cache, no-store
Pragma: no-cache
Date: Fri, 29 Mar 2019 00:38:11 GMT
Connection: keep-alive
{
“identifier”: {
“type”: “dns”,
“value”: “irmtraut.spdns.de”
},
“status”: “pending”,
“expires”: “2019-04-05T00:38:11Z”,
“challenges”: [
{
“type”: “tls-alpn-01”,
“status”: “pending”,
“expires”: “2019-04-05T00:38:11Z”,
“challenges”: [
{
“type”: “tls-alpn-01”,
“status”: “pending”,
“uri”: “https://acme-v01.api.letsencrypt.org/acme/challenge/VhTeLQ81UQ7d49uM7KxpCeSxchHYPzxnKt6a6Yc_xJc/14142918359”,
“token”: “ph0Vamp8NjNvtgj2VEsTdFTLmV5WYHO4q9OqKKSby88”
},
{
“type”: “http-01”,
“status”: “pending”,
“uri”: “https://acme-v01.api.letsencrypt.org/acme/challenge/VhTeLQ81UQ7d49uM7KxpCeSxchHYPzxnKt6a6Yc_xJc/14142918360”,
“token”: “JeGImh5LwkOqHAkSEdnLPBwnC2TileBQTwAceejp-vQ”
},
{
“type”: “http-01”,
“status”: “pending”,
“uri”: “https://acme-v01.api.letsencrypt.org/acme/challenge/VhTeLQ81UQ7d49uM7KxpCeSxchHYPzxnKt6a6Yc_xJc/14142918360”,
“token”: “JeGImh5LwkOqHAkSEdnLPBwnC2TileBQTwAceejp-vQ”
},
{
“type”: “dns-01”,
“status”: “pending”,
“uri”: “https://acme-v01.api.letsencrypt.org/acme/challenge/VhTeLQ81UQ7d49uM7KxpCeSxchHYPzxnKt6a6Yc_xJc/14142918361”,
“token”: “tBaUbp5KXD-U58fOoViSK13Kj06-6Eaa6Jdw1jxtlv0”
}
],
“combinations”: [
[
2
],
[
0
],
[
1
]
]
}
2019-03-29 00:38:11,147:DEBUG:acme.client:Storing nonce: 4DDM8d7dcV8Gyu_V_cv22Mo5oZ38X94kEzrbqxcq8iY
2019-03-29 00:38:11,149:DEBUG:acme.challenges:tls-alpn-01 was not recognized, full message: {u’status’: u’pending’, u’toke$
2019-03-29 00:38:11,151:INFO:certbot.auth_handler:http-01 challenge for irmtraut.spdns.de
2019-03-29 00:38:11,152:DEBUG:certbot.plugins.webroot:Creating root challenges validation dir at /var/www/html/.well-known$
2019-03-29 00:38:11,178:DEBUG:certbot.plugins.webroot:Attempting to save validation to /var/www/html/.well-known/acme-chal$
2019-03-29 00:38:11,180:INFO:certbot.auth_handler:Waiting for verification…
2019-03-29 00:38:11,181:DEBUG:acme.client:JWS payload:
{
“keyAuthorization”: “JeGImh5LwkOqHAkSEdnLPBwnC2TileBQTwAceejp-vQ.vRv29Yf4HBL6Ts3JRjKVA5vkNg8RX8NJ7QoaGwybt64”,
“type”: “http-01”,
“resource”: “challenge”
}
2019-03-29 00:38:11,219:DEBUG:root:Sending POST request to https://acme-v01.api.letsencrypt.org/acme/challenge/VhTeLQ81UQ7$
{
“header”: {
“alg”: “RS256”,
“jwk”: {
“e”: “AQAB”,
“kty”: “RSA”,
“n”: "sqsXtcxkh2bEyrHRj9Ez2lkhDqAzdIOMNb99qxawB5GFvpKqnexsmrGMVzvC1I0fYcneWMhu3GpqWt0OIgG7DLDHFKV4zdKEalFQLmT3sdYZsA$
}
Sorry, das stimmt natürlich. Die Nextcloud läuft auf einem Pi mit externer Festplatte. Prinzipiell läuft die Nextcloud sehr gut und aufgrund der vielen gespeicherten Daten wäre ich froh, wenn ich gerade keine Neuinstallation durchführen müsste 
Könnt ihr mit dem log etwas anfangen?
Vielen Dank für eure Mühen!!
Fabian