Apps.nextcloud.com down only for me

Dear community,
I have problems reaching the app store from my ip address. I know the app store is up and running fine.
I have set up a nextcloud server with a nginx gateway. It worked fine until two days ago. There I realized, that I have problems connecting to apps.nextcloud.com. It appears that my whole ip address is now blocked by some sort of fail2ban.
Does anybody know how long I will be blocked?

My nextcloud log was spammed with the following message:
{"reqId":"XXXXXXXXXXXXXX","level":2,"time":"2020-04-05T11:11:53+02:00","remoteAddr":"XX.XXX.XXX.XXX","user":"username","app":"appstoreFetcher","method":"GET","url":"/nextcloud/settings/apps","message":"Could not connect to appstore: cURL error 6: Could not resolve host: apps.nextcloud.com (see http://curl.haxx.se/libcurl/c/libcurl-errors.html)","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0","version":"18.0.3.0"}

I guess my server made to many requests in too short time…

What would be a good starting point to debug this?

Related topics here which did not help me:


Thanks and Best regards
Georg

Solved by restarting my FritzBox. something with the DNS must have been wrong…
Same problem here: App Site not available

Edit:
Problem came back again. This time a restart of the FritzBox did not help…
I changed the DNS Server in the FritzBox to
IPv4: 8.8.8.8 and 8.8.4.4
IPv6: 2001:4860:4860::8888 and 2001:4860:4860::8844

Now I can reach out to apps.nextcloud.com again. Definitely a FritzBox problem…