This might be relevant to your issue.
From reading eM Client threads back in eg: 2024 on Kerio connection problems or crashing problems even with the older Kerio connect 10.0.5, that was traced back “directly with the Kerio EWS implementation which was bad” as @Michal_Burger posted in this thread link and users found “changing to an IMAP setup” fixed the problem as
@a.semenets posted below in that same thread.
So suggest to try an IMAP setup rather than EWS setup and see if that fixes it. Just a thought.