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loviedovie - it could be a manifestation of the same problem, the PIs that were changed was because they manifested the problem, not because of any exhaustive analysis of the structure or code of each every PI
Try running without any PI's, using the --ignore-plugins option see ==>>
calibre command
If that works then you'll have to remove all PI's (don't worry you wont lose your PI settings - but to be safe backup your config directory) add them back one-by-one until you find the culprit and report the problem in its PI thread.
If ignoring all the plug-ins doesn't work I'm out of ideas, you can report a bug here ==>>
Bugs : calibre
BR