This one was a treat. Worked flawlessly in preview, of course.

The admin approved browser form had some buttons that were switching views. The IPFS error was:

An editing action referred to a field or control that cannot be found in the current view.

The log files helpfully supplemented this with:

The StateManager is disposing and calling ReleaseLockedStates() (Count=0) 

I added new buttons and was able to switch views without error - the original buttons had similar actions and had been copied / pasted from one view to the next - they'd maintained the same control ID. So, I changed the names on the buttons - just added "a", "b", "c" etc.

And the error went away. I don't know whether to be happy that I found the issue, or sad that it was so hard to find and the error messages were so meaningless.