Bookings - service notes with null in place of a link

Hi

We create bookings using the Graph API with application permissions (unsigned customers create the bookings).  As part of the process a link is included in the service Notes field so that when the internal users look at a booking in the calendar they can see (and copy and paste) a link to the relevant case in a case management system. The actual text that is assigned in the application is 'Access Case: https://[thelinkgoeshere]'  .

The problem I have is that some users can see the added link text while others see 'Access case: null'.

I thought the users might have different levels of access in bookings - but I have some users who can see it and some that cant - but they are all set as Schedulers.  Changing the level of the user from Scheduler to Administrator hasn't made any difference - they still see the 'Access case: null'

Is there some setting in bookings/ O365 etc that might account for why some users can see the link but others cant.   (for clarity 2 users can look at the same appointment - 1 can see the link the other can only see 'Access case: null').  Also for clarity the link is never an actual link, just text - they have to copy and paste.

 Thanks,