Cryptomatte error

I have been working on a CG project (not many 3rd party fx but lots of comping passes) for some weeks with no problem but the other day I got the error "bad parameter in effect callback (26::285) and then my comp window went black. When I looked into the layers, Extractor wasn't pulling out the correct passes - most were black, some were attributed to the wrong pass and my cryptomattes were completely scrambled. My renders are multi layer exr sequences. The weird thing is that when I import a single frame as a still, everything works as expected. The same frame as part of a sequence: completely fried (see attached). Any idea what's wrong? To simplify things I imported one sequence into a new comp and it still happens there: go to (for example) frame 100 in a sequence and it's knackered but import frame 100 from the same sequence as a still and it renders fine. 

I'm on the latest AE 2022 but I tried opening it in a copy of AE 2021 with no 3rd party plug-ins and it's the same there. I'm on Windows 11 but this file has the same problem (and error code) when opened on my Macbook Pro so it's not hardware related.