I've noticed this for quite a while, but don't know if it's been fixed in v7459 or later.

Basically, people will create a folder with a space at the end of the name. 

Example:

[2020.07.16] 09:58:32.878 [xxx.xxx.xxx.xxx][62494058] command: tszr CREATE "INBOX/NEW SERVICES " [2020.07.16] 09:58:32.878 [xxx.xxx.xxx.xxx][62494058] response: tszr BAD CREATE  invalid arguments

On Exchange, it will automatically remove the space and happily go about it's business.  I just tested on Exchange 2013 to confirm.  With SmarterMail it will error out as above and not sync that folder, but can also cause Outlook to hang on checking other email folders as well.  Sadly, Outlook will not display the error, and customers have no clue until something breaks.