Apple Mail freezes or crashes during IMAP sync with gmail

I have this problem that bothers me a few weeks now. In my Apple Mail on MacBook Pro I have 4 Mailboxes. One of them is Gmail synced via IMAP.

When I open the app everything works fine for about an hour. Then an exclamation mark next to my Gmail inbox appears saying "Too many simultaneous connections". This is non-sense because this is the only app accessing the e-mail (I know its creating more connections in background but...).

The problem is that after this hour the whole Mail app is kind of freezed. Sending e-mails stops at 80% and wont finish (even all other mailboxes) and app silently doesnt synchronize all mailboxes. From time to time the whole app crashes completely.

Do you have any ideas what could be wrong? Where to look for more details about this? Anyone with similar problem? Thank you!