Great, thanks for the reply.
To close the loop, it was indeed a bad ram chip, running stressapptest showed a ton of errors within the first minute. Interestingly, after finding and removing the bad RAM and running the “Check Particles” job (on the particle stack extracted with the faulty RAM), the 2D classification would run but would yield very strange looking circular patterns. So, clearly there were some errors which the job could not catch. Re-extracting the same stack with good RAM seems to make everything work.
Best,
Klim