This error seems to come in waves, I thought it had disappeared with v10.4.5298 but came back. It still occurs with V10.4.5326.
Very annoying, this error got so bad yesterday that the Inbox on one account was inoperable for a couple of hours.
We have to wait until V11 comes out and see if the new protocol with Microsoft accounts fixes it. See Michael_Burger post here: Chronic problems using eM Client with hotmail and outlook - Mail - eM Client