Yes that also used to happen to me using V10 on PC & Mac with a Microsoft IMAP Live account. Have you tried the latest 10.4.5674 if you don’t have that already to see if that fixes the problem.
Testing V11 Beta this does not happen on Pc or Mac. So if it still happens on 10.4.5674 no doubt eM Client will do an update to fix it.
You can try the Beta if you like and read about it via the following link if you want to give it a go.
If you do try the Beta “make a manual backup first” via “Menu / Backup” incase you want to restore for any reason. Also “close eM Client” before updating