This just happened to me with the water leak event. My residential rental unit is a single family home. The property owner lives in a regular residential. Landlord has max handiness and went to repair the broken tub and sink. Once she repaired the last item, instead of marking that task completed on the event (with the next task being to mop all the puddles), the puddles disappeared along with the event. I received a notification that the event had been ignored and my unit rating was going down. I play on PC.
Edit #1: Pet Adoption Drive started immediately after the failed water leak and was successful. "Pet Cats and Dogs 5/5"
Edit #2: Next water leak event, I tried using the expensive contractor. Despite their best efforts, they failed.
Edit #3: This time, as soon as I got the notice that there was a water leak, I saved my game so that I could better test. I went to the unit and tried only repairing 1/2 leaking appliances, and then I mopped puddles and left the second one. There were only 5 puddles and I needed to mop 7. I was hopeful that the game bugged the first time because I repaired the plumbing right away and didn't have enough puddles to mop. Unfortunately, that was not the case. As soon as the 7th puddle was mopped the event failed without letting me repair the sink. I exited without saving, and I tried the expensive contractor again. Despite their best efforts, they couldn't fix the leak. Next I tried the cheap contractor, unsurprisingly, they didn't fix the leak either.
I do use UI cheats extension and MCCC, so I exited the game without saving and tried removing UI cheats to see how that might impact the event. No dice. Once the 7th puddle was mopped, the event failed. I couldn't repair the objects with 5 hours remaining. I checked, and there wasn't an exception generated by MCCC.
I tried removing MCCC, so my game is now mod / CC free. Vanilla game still resulted in failure. Here's a link to my vanilla save after the maintenance failure occurred.