I've had bugs go away when I added `print("working fine until here")` to the preceding line. So if someone told me "this line is needed but I don't know why", I wouldn't even blink.
My coworker took down our site briefly by removing an html comment that said "don't remove this comment".
Load bearing print statement!
I've had a few of those, I think they're usually a symptom of stack corruption.
Or a concurrency/timing issue, where the delay of the I/O changes things just enough to make them work on your setup.
Back in the day the QA department would veto a release candidate of our firewall product due to performance degradation if a network cable in the testing equipment was bent too much during validation runs. Rearrange the cable and next test run would pass.