[Darryl Ramm]

This is extremely unlikely to be related to any of that.

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Looks like a garden variety session corruption.

Either roll back to the version that works.

- or -

Working on a copy of your current session (copy from the OS) try identifying what media file is corrupted or causing problems and just replace that file in the session with an older version or try deleting it and recreating that one file content if needed. Can you play that file in the browser/OS? (I'm guessing its' corruption in a single file but might be more, might be missing files or directories or the session file itself corrupted etc. Try replacing files and see).

-or-

Try an import into a new session. that might work or might fail at some point and provide a clue.