Not on a regular basis my Nexus Ultimate informs me I am using a trial period version even though it still has until December this year to be viable for free updates. Exiting it and then calling it up on a shortcut rectifies it back to normal.

So, 'not on a regular basis' means 'very infrequently', right?

Did this just start happening?

Anyway, not sure why that happens, but I don't think you need to exit Nexus Ultimate to rectify it: if Nexus Ultimate thinks it's NOT registered, it will show the Registration tab in Preferences again. Going to it and clicking the 'Register' button should set it back on track.