Thank you for your message. This is quite unusual behaviour that you are describing.
I would first recommend looking in the Audit Trail for your CMS to see if you can locate a log for that Display and when it was changed from Authorised to not Authorised.
Below is a screenshot of the Audit Trail logs from my own test CMS:
I de-authorised and then authorised my Display with the ID 36. You can see that when I did that, it created an Audit log. The first log with ID 2322 shows that my User (danielbw) made a change to a Display with the ID 36 and that Licensed was set from 1 to 0. When I authorised you can see that the licensed value was set to 1 again. I would recommend seeing if you can see any entries in Audit that might shed some light on the Display not being authorised.
If you find that it happens again unexpectedly, make a note of the time and date you discovered this and check the logs for more information. Feel free to pass on anything you find that might help explain what is happening.