NAV2016 - Corrupt Ribbon

I have a client with users on a Terminal Server, where one of the users 2 to 4 times a day suddenly gets a corrupt Ribbon. The user typically notice that the New button disappears, and that she can't switch between the Home & Actions & Navigate tabs. She can still switch window in the Role Center and even open new windows using the left-hand side menu, but the ribbon is always corrupt. A few of the actions works – typically Search and Links and other system buttons. Other customized buttons rarely works.
She solves the problem by restarting her NAV client, but she is rather disappointed it should be necessary.

They are using NAV 2016 CU9 (build 46290 - server & client)

Any ideas, besides deleting her personalization metadata?