Same problem with our nextcloud (21.0.1) running on a Synology DS218+. I cannot access the App Store / update apps anymore and the checks & warnings on the admin page also don’t work.
Looking in the logs I see a lot of errors from the “internet_connection_check” app, that is desperately trying to reach different servers, but fails:
GuzzleHttp\Exception\ConnectException: cURL error 28: Resolving timed out after 30000 milliseconds (see https://curl.haxx.se/libcurl/c/libcurl-errors.html) for http://www.nextcloud.com/
As I haven’t changed anything on the network side within the last few days, I’m not sure what’s causing this… after rising the timeout in the Client.php (as described earlier) I don’t the see the errors in the log anymore, but the server check on the admin page still doesn’t work… Any other ideas?
edit: I tried some more things and noticed that my local DNS server (AdGuardHome) seems to have blocked/discarded some local DNS queries… I disabled that and now everything is back to normal. 