Permission denied for external users with usertype member

We have created a multitenant organization and synced a few user between the tenants. Almost everything is working, except access to planner in a connected tenant. 

When navigating to a sharepoint site of a connected tenant everything looks fine. If opening planner inside the site we get access errors. This is also true if we navigate directly to tasks.office.com/[domain].

After some testing it seems to be that external users synced thru cross tenant sync in combination with multitenant organizations are the problem. Per default this users get the usertype member instead of guest, which is a good thing, but the usertype is the reason why it is not possible to view plans. For testing propose I change the user type to guest. In this case the inline Planner view in sharepoint and tasks.office.com was working. Switching back to usertype member, the access is denied again.

Another test with a tenant not member of the multi tenant organization showed the same behaviour. Working with usertype guest, not working with usertype member.

So I think there is some problem with the authentication or authorization in this specific case, or am I missing something?