It’s worth trying to see if you can get eyeballs on the room immediately above that location. If you have multiple floors windows are usually placed in parallel, one floor above the other. So it may be not a plumbing issue, but a window above could have a leak from the exterior that’s traveling downwards. Or the roof. I’ve seen leaks presenting evidence 20+ feet from the source before. They can take really unexpected routes through a building.
Ha! A buddy of mine was a cable guy for years.
I’ll bet you $5 if it’s not your bathroom then the cause is the fiber installer poked a hole through your exterior wall and didn’t properly seal it.