Commode flushes fine, sometimes a little water comes back in and sometimes it fills up. It was full 4 hrs ago and I looked and the bowl was empty! Can't find any water anywhere. This bathroom is on the third floor, no wet ceilings, nothing....the other commodes work fine.
Check inside the tank and make sure the small plastic hose from the fill valve is properly connected to the 1 inch plastic tower in the center of the tank.This helps put the water in the bowl after a flush.If this is ok then my best guess would be a small crack in the china letting the water seep into the inner channel and going down the drain.That would be rare but nothing is not impossible.
If the bowl was full and without additional use it emptied, this often means a siphonage is occuring. A string of something is in the trap way. This is usually occupied by a drain line stoppage which seems unlikely on the third floor but possible. If it's not the refill tube you may want to pull the toilet and look up in it with a mirror. Also check your drain line by runnning a line from the stop into the drain.