Sometimes when running Python nodes at the same time it can happen that a node just fails with “stopped executing”. I wasn’t able to pin-point the exact issue but I think it’s when 2 nodes at the same time are loading / outputting data, then one of the fails.
WARN Python Learner 0:579:0:423 Execution canceled
And log file doesn’t say anything more.
So there for sure something is going wrong (not 100% stable) with the python nodes.