I tried this with mongosh and I cannot reproduce it so maybe it’s related to data in your collection? Does this happen when you run this explain on a different collection?
This could be related to COMPASS-4944 and one way to check would be to try this in the legacy MongoDB shell (mongo rather than mongosh) as it’s not based on the Node.js driver and might handle invalid UTF-8 differently (showing where the error is).
I suspect that collation is maybe a red herring (as in the invalid document is skipped with simple collation and matched with specified collation so it’s only encountered with one and not the other). Do you get this error at all without explain?
Asya