1. log in to browser A as user X
2. log in to browser B as user X
3. in browser A, create an appointment for customer 1
4. in browser B, create an appointment for customer 2
5. in browser A, delete the appointment for customer 1
This will trigger a 'Transaction rolled back because it has been marked as rollback-only' error
This is occurring because each time a customer or patient is selected, it updates the selection history, accessible via My Recent.
At steps 3 and 4, the sessions for browser A and B have different copies of this history, so when browser A goes to update it in step 5 whilst deleting the appointment, the update rolls back. This rolls back the appointment deletion as well.
The workaround is to select a different customer or patient. This forces the browser A session to update its copy of the selection history