I have tested the same with FRP 5.0.7 and EPO 5.9.1 and I have not seen a similar issue here. I was able to remove and add exempted devices successfully.
We would need to troubleshoot this issue further. I advise you to open up a support ticket with McAfee Technical Support by choosing the point product as FRP and we would assist you as soon as possible.
For better understanding kindly share this community forum link on the ticket.
Was my reply helpful? If you find this post useful, Please give it a Kudos! Also, Please don't forget to select "Accept as a solution" if this reply resolves your query!