[DCP-o-matic] Failed SMPTE validation on Sony projector

We had a very strange problem with a short DCP this week at a multiplex cinema with Sony projectors. The DCP was made with DOM 2.14.54. It was 2K Flat, SMPTE, unencrypted, 25fps. It was 2 mins long. The DCP was due to play in 3 different screens. In one screen, it played fine. In the other 2 screens, the same DCP ingested fine but then failed at the "validation" stage. In one of these screens, after repeated attempts, the DCP did finally validate, but then wouldn't play (as in when you pressed the "play" button, nothing happened). The same cinema has in the past week successfully played other SMPTE DCPs made with exact same version of DOM and same specs (2K Flat, SMPTE, 25fps, unencrypted). All three screens have Sony projectors. As usual with these kinds of things, I have of course tried to find out the model number of projectors, firmware version etc but am unable to extract this information from the cinema staff, who are rushed off their feet. A couple of questions: 1. I had understood that this issue was resolved a couple of years ago. https://dcpomatic.com/forum/viewtopic.php?f=2&t=1214 Has anyone else seen validation fails on Sony projectors since DOM 2.14.x? 2. What even is "SMPTE validation" anyway? My understanding of "validation" is that it's a content integrity check (hash check etc). However, I thought that happened at time of ingest and ingest would fail if hash check fails. This problematic DCP is ingesting OK, but then fails later at "validation". "Validation", I am told, takes a long time (1 hour or so for a feature) and can only be run when the projector is not playing anything. That suggests it is reading a lot of data from disk. Again, that sounds like a hash-check. However, the cinema said their projectors only perform this extra validation for SMPTE DCPs, not Interop. So, if validation means what I think it does, why are Interop DCPs not being hash-checked? Or if "validation" means something else entirely, what on earth is it? I hope someone else may be able to shed some light on these mysterious events! Jim