Can't figure out what to do next with this shower issue

[nd23rin]

We have a some water leaking from our upstairs bathroom to the area below it (1st floor kitchen). The strange thing is if you just use the shower once a day or so it never starts leaking. If you use the shower multiple times in the day or for an extremely long time it starts to leak. I cut the drywall in the kitchen so I can see the little area of the subfloor where the water is above it. We haven't used the shower since but about a week ago a ran one of those little endoscopic cameras from amazon down the drain and there was a lot of hair in there along with standing water visible from the drain cover. The standing water seems to be around 8 inches down. I ran a drain auger like 25 feet down and snaked it and some debris did come out, however the standing water is still there.....and it STINKS. I had my wife tap on the water spot below and it actually seems to be right in the wall dividing the toilet from the shower (the shower drain and toilet are probably 8 feet apart I guess), but 100% the leaking only happens when using the shower and only if it is used for a certain amount of time in a day or so. Any ideas what might be happening? I tried flushing the toilet and checking the water sitting in the drain and although it flutters a little it doesn't move drastically.

 

[CT-18]

Are you sure the standing water is not the P trap. You may have issue with grout lines that is causing a leak. Did you try running the shower with no one in it to see if it leaks

 

[nd23rin]

Thanks for replying....yeah I guess it could be the p trap. I didn't know it was normal for it to be visible (and smellable lol). I haven't considered grout lines. It's important (maybe) to note that the shower floor is rough stone tile. Honestly I don't know the official name for it. I don't remember 100% if we tested it without a person in it. Last time we tested it was after we re-calulked everything. We ran the shower for 10-15 minutes and thought it was fixed. Then 8 hours later someone used the shower for 10-15 minutes and almost immediately we saw drops of water coming through the hole I cut in the drywall. I'm obviously not an expert by any means so in my head I envisioned something that was supposed to be draining was moving so slow that it was accumulating causing the leak.

 

[Geofd]

Test the tile,grout,+,pan 1st block the drain with a plastic +,rubber test plug in the drain, fill buckets of water from another sink don't use the water from that shower,let the water sit in the shower overnite fill it as high as possible start there you can buy a test plug (2") at home Depot it pushes into the drain then you tighten the wing nut

 

[GReynolds929]

Could also be a leaking shower arm. You could take the shower arm out and cap the drop ear to see if the leak still happens.