Not able to send/save E-Mails via Roundcube Webmail

Description of the issue: When I try to send or save an E-Mail via Roundcube webmail, it just loads for some time and then the loading icon disappears.
How can this issue be reproduced?

  1. Try to send or save an E-Mail via Roundcube Webmail

Expected result: Email is sent/saved.

Brave Version( check About Brave):
Version 1.38.109 Chromium: 101.0.4951.41 (Official Build) (64-Bit)

Additional Information: I notified my hoster about the issue on 19.04.2022, 20:26, the last E-Mail was successfully sent via Webmail on 17.04.2022, 17:50.
There has to be an update in between that most likely caused this issue.
It’s working with other Desktop Browsers and also with Brave mobile.

(I granted all possible permissions to the website and disabled brave shield, but still not working)