Hi,
We have been synchronizing some new users to the CRM (Custom app similar to Customer service hub) so that they can track some appointments to the CRM. For most of them, setting the category as Tracked to Dynamics 365 is going to be the way to go. For one of them, we get a warning message and their appointments can get synchronized to the CRM. They turn darker blue, but they are never added.
That's the warning we are getting: 
The link on Learn more is not available anymore and we can't seem to find documentation about it.
Do you guys have an idea of what might be our issue?
