Friend was doing some C41 for me, evidently a little blix got in the developer, everything was blank, he thought it was an exposure problem, for about 2 minutes until we noticed there was no edge printing as well. Lost 2 rolls of nudes, well the film was nude.
Have had some oddities, was reusing bottles and the cap on the bleach for E6 had some silver deposits, which appeared on the film, in pieces, Kodak looked at the film and figured it out very quickly.
Had some odd objects in the sky area using Konica IR 120, even Konica could not figure that one, sent one negative to Japan-- no explanation.
Agfa admitted they published some wrong times and I had some very thin negatives, their tech guy admitted it, so you have to give them credit for that.
Any time someone screws up some negatives, it is really bad, IMO. My regular lab processed C41 B&W, scratched the negs and turned off Digital Ice because they did not know you could use it with C41 B&W, then, though I told them not to, they cut the negs, so I have a lot of re-scanning of short strips to do.
Dilution problems, I am pretty good with math, but a friend using my darkroom was off my an order of magnitude with HC 110, blank rolls again.
Time and money are one thing, but when you ruin negatives/film there is no going back.
FWIW, more labs have screwed up than I have, some take care of their equipment, and some do not, liability in Ohio is limited to replacing the film.
Regards, John