Hi Everost,
Based on the description issue is most likely to lie with the Mac Outlook client side. I would like to know have you tried to contact our Microsoft community Office for Mac support. If not, then I’d like to involve our dedicated Outlook for Mac support team in solving the issue for you, because the engineers there are more professional in Outlook for Mac related issues . Please post your question in this forum and our engineers there will be glad to assist you.
Your patience and cooperation are highly appreciated.
Best regards,
Shyamal