Found a new .htaccess rule but not sure how this fits in with the nginx config. Seems the nginx config offered in the nextcloud docs is quite buggy.
RewriteRule ^ocm-provider/?$ /index.php [QSA,L]
EDIT:
Found a fix. So you probably need to revert some fix you did in a previous version if there is this construction in your nginx config. Where there is:
oc[ms]
replace with
ocs
and restart nginx