Nearly the same problem when I have again upgraded from 10.0.1 to 11.0.1.
Two things to redo and it works back (that would be great it is somehow if possible handle in future nextcloud releases):
-> Add value '/^DAVdroid/' and/or '/^DAVx5', to the file /lib/base.php
$incompatibleUserAgents = [
// OS X Finder
'/^DAVdroid/', // not necessary if only DAVx5 clients
'/^DAVx5/', // not necessary if only DAVdroid clients
-> Add the 3 following lines to the .htaccess file which is at the root of the nextcloud directory:
SetEnv no-gzip 1
I did these two modifications and started with the .htaccess one. Only modifying .htaccess was not sufficient.
I did not try to only modify /lib/base.php.
I was upgrading from 11.0.0 (that’s what the web installer installs) to 11.0.1. I deleted my installation to make a fresh install (11.0.0) on a subdomain so everything is at root and I don’t have those errors, services are recognized by DavDroid. Are we supposed to dedicate a domain or subdomain to nextcloud ? (that sounds logical in a sense but I didn’t know it was mandatory)
Now I have other issue (basically : absolutely nothing is synchronizing, and no calendar import are working) but I’l give a try to upgrade to 11.0.1 again first and see if anything gets broken again.
Thank you @philippeVerney I already stumbled on one of your post about the problem with gzipd output and header sent with a 0 size so I disabled compression when I installed
I’ll try to set this incompatibleUserAgents variable.
Edit : Thank you @philippeVerney the calendar is now synchronizing - and contact too but not before deleting all my contact list first.
After the upgrade the .htacces modification that prevented compressed output from the server has been erased though (but now all seem to work ?!)