This happened to us just this past week. Something totally unexpected and undetected. Patsy was vacuuming the bathroom in our bedroom and afterward told me a piece of grout pulled up from the tile floor. I went to look and it might have been a quarter inch piece of grout, not enough to be noticeable to any man but enough to worry the hell out of a woman. I suspected moisture but neither one of us had ever seen any water on the tile around the commode. Just to satisfy her curiosity, I removed the crawlspace door and looked underneath the house. The entrance luckily was just a couple of feet away from the commode. Here's what I found.but some larger things thrown in,

The commode has been leaking for some time! Mold and mildew had already covered the bottom of the subfloor.
To make a long story short, this past Friday, Servpro, a water mitigation company removed the ceramic tile, the durock under the tile, and sprayed the mold/ mildew under the house and then will scrape / scrub off the remainder this week. They left several fan / heater type machines in the bathroom and under the floor to attempt to dry the plywood subfloor out. I asked why not just tear it out and replace it with new plywood. Their reply, "the insurance requires us to try to save it first."
But here are some pictures of our mess.
Before:

Our bedroom used as storage space:

The wet subfloor with a "flood cut" on the beadboard paneling:

The attempt to dry. This shows progress in drying the subfloor.

The durock concrete type material used under the ceramic tile:

I'm not sure how to prevent this from happening. After our daughter's stroke in April 2019, she had to move back in with us and we had all the commodes changed to the larger handicap style. So this commode was put in place with a new wax ring in early November 2019. There was never a sign of a leak above the tile, foul odor, wobbly commode, soft spot in the floor, nothing to cue us we had this going on. The only wet area was under the durock and on top of the plywood subfloor. The top of the durock was dry.
I found some water detectors on Amazon I'm going to try just for future peace of mind. The Servpro crew said they recommended checking the wax seal once a year. Who does that?
Probably me from now on.

