Outlook gets stuck in "loading Profile" after adding a Shared Cloudmailbox

Question

We run a hybrid solution for our mailservers, some are still on prem and others already in the cloud. The mailbox was initialy an on-prem mailbox and then was moved to Microsoft 365. This change didnt cause any problem, however when i tried to add another cloud mailbox my outlook client gets stuck with the message "loading profile". During this state, i am unable to remove it and i had to delete the old profile and create a new one to access my mails.

Also after i have added a new profile outlook didnt start at all, which meant i had to remove my whole user profile and start from the beginning again.

I was able to add the mailbox with the function "open additional mailboxes" but there are some features missing, like rules and notifications are missing which i need access to.

For some of my colleagues there werent any issues. All colleagues have a on-prem mailbox, just like myself.

I have already tried:

the manual set up

Different laptops

different options in the advanced set up (Microsoft 365, Exchange, etc...)

• checked permissions in the AD
• checked attributes in the AD and Exchange

waited about 6 hours on a different laptop with outlook loading

The current version im using is 2402 Build 16.0.17328.20346 64 Bit

In the screenshot you will see that it gets stuck during the "loading profile"