Here is what makes everything work ok:
In the cloud.conf (Seafile) I deleted the "http2" in the server part that listens on port 80 and redirects.
It looks like this now:
server {
listen 80;
listen [::]:80;
server_name cloud.mydomain.com;
rewrite ^ https://$http_host$request_uri? permanent; # force redirect http to https
# Enables or disables emitting nginx version on error pages and in the "Server" response header field.
server_tokens off;
}
Noe everything works fine.
I am not sure what advantage / disadvantage http2 had, to be honest.
Maybe the http2 part should only be inside the config part that configures the 443 access?
Well, this did the trick at least.
I am still interested in the config that you posted on gist though.
It looks really tidy and well organised.
So I would still like to know if I can leave Nginx running for letsencrypt bot to work ;-))
Greetings, Chris