Hmmm again! The whole purpose of IR tests is to detect small, or very small, (electrical leaks), often due to moisture/water - so if his theory is that a water-related electrical leak may be happening, it would seems pretty surprising if he did not do such tests.Gah! Although I mentioned this to him when he arrived, I forgot to ask him if he did that test, balls! I have a feeling he didn't as the whole focus seems to be on finding whether or not the shower is going to earth...I'm a bit confused by that. Although it would probably be necessary to rip up flooring to deal with any water leak that was detected, if his theory is that water in a JB is causing an (electrical) 'leak', I would have expected him to confirm (or dismiss) that possibility by undertaking Insulation Resistance tests on all the relevant circuits, which would not require any interference with the flooring.
In fact, more generally, given the uncertainties/mysteries around and the nature of your experiences/concerns, I would have thought that IR testing 'everything in sight' would probably be an early step in the investigation of this possible problem.
Kind Regards, John