Some External Parties Cannot View Shared Files in Microsoft Teams Shared Channel

Hi,

We have setup a team with some shared Channels, and did the whole configuration (B2B Direct Connect both sides) to let an external  company (CompA) (MS365 tenant) access it.

It worked fine, but since some weeks 'some' people can not access the Files tab anymore, they are receiving this error

Removing these people from the shared channel and adding them after can solve (temporary) the problem or they do not even see the files tab.
They have tried different teams apps, same behavior.

Other people of the same external company can access the files without any problems.

To our shared channel I have added a second external company (CompB) , but these people do not have any problems.

Anyone any clue what could the cause of this Issue ?

Regards

Kurt