There is a bug in the current Rainloop Nextcloud plugin based on Rainloop 1.15.0.
This bug is fixed in the latest official Rainloop 1.16.0 release (https://www.rainloop.net/downloads/).
Result:
Sieve is not connected properly therefore filters can not edited or applied anymore
Reason:
SSL-Crypto connection is not requested/established by Rainloop.
There is a bug in the current Rainloop Nextcloud plugin based on Rainloop 1.15.0. This bug is fixed in the latest official Rainloop 1.16.0 release (https://www.rainloop.net/downloads/).
Result: Sieve is not connected properly therefore filters can not edited or applied anymore
Reason: SSL-Crypto connection is not requested/established by Rainloop.
Bugfix/Commit (can be maually applied until fixed/updated release for Nextcloud is available): https://github.com/RainLoop/rainloop-webmail/commit/c2fc21afedb31aecc3fc21265e01c33382dd67aa
Update for Rainloop was already requested in https://github.com/pierre-alain-b/rainloop-nextcloud/issues/243
Cheers! :-)