"What should the next steps be if any?"

Maybe hire a different plumber?

Not use the tub?

Use the tub and hope for the best?

I was looking for more of a response to why the leak happened and why is it not leaking anymore even though the bathtub is being used regularly. And, any potential solutions/recommendations for this issue.

Aaah,why didn't you say that before? It happened because a stem packing dried out and let water leak. It isn't leaking anymore because as plumber was checking,he didn't see a leak but tightened packing nuts "JUST IN CASE". which turned out a good guess.

Plumber didn't do anything, he just tried to re-produce the problem first by dumping water into the bathtub so he can move forward, but he was unsuccessful. Even he was shook to why water isn't leaking again. Did it just got fixed on it's own then? Should I ignore it until it leaks again or do you recommend something else? Again I am seeing no discoloration in the ceiling if the water was seeping inside.

"Did it just got fixed on it's own then?"

Not likely, which was why the suggestion to try a different plumber.

Both my kids have caused a similar leak by leaving the shower curtain liner on the outside of the tub while showering. We caught it before they were out of the shower, so no denying it. It was just carelessness.

Is the overflow for the tub installed properly?

This happened to us with our shower. Do you have a hand held shower head attachment and an on/off- hot/cold lever handle in your shower? And is it possible a stream of water was sprayed at the lever handle wall at some point during the shower? There is possibly an opening on that on/off lever fixture along the wall edge, for some reason (ventilation?). It isn’t designed to have a constant stream of water sprayed directly at the wall there. Apparently, on the interior wall of the on/off handle there is some waterproof barrier set up to handle some dripping, but not a steady stream of water aimed at it. We solved our problem by beefing up the interior wall’s water barrier and avoiding spraying that wall directly when cleaning the shower. (I apologies if I’m using the wrong terminology. I’m not a plumber.)

Filling the tub does not duplicate the conditions of showering. If you eliminate the possibility that the shower curtain was not properly used, you still need to check the shower riser connections for leakage and also spray the shower walls to test for caulking failurew.

"someone was showering in the . . . . tub"

"why is it not leaking anymore even though the bathtub is being used regularly"

Although the overflow is a common leakage point for too-high waterline and kids making waves in baths, I don't think anyone showering would let water get above the overflow. And if there was a problem with the drain flange, say with standing weight flexing an acrylic/fiberglass tub that the plumber couldn't emulate, that leak would occur often now. And a mixing valve escutcheon should have a gasket as well as highly unlikely a steady stream of water is focused on it during a shower, but I suppose that is a possible leak point.

More than likely, given your above statements of tub and happened only once, I would agree with the shower curtain hypothesis. Either draped outside, or inside and left the end open on either front or back, and water streamed out onto the floor. Either the connection of tub to floor caulk is not adequate, or water travelled to under nearby toilet and found the nearest light fixture on its way down.

Unfortunately, I speak from experience on that exact scenario, multiple times. The root cause was found to be "oblivious teenager." If only the once, maybe a couple times, don't worry about mold, as the water found a way out. Just leave the trim/canopy off the light for a couple days to allow better airflow through the gaps.

I appreciate all the responses so far. To add some more info to this problem, this bathtub has a glass sliding door so we can eliminate the scenario of curtain being left outside the tub wall. We have no kids in the house, it was an adult showering at the time of the incident with no handheld shower but with a fixed top head shower. There was no water on the bathroom floor when this happened. I am guessing something happened from the inside. This bathtub is still being used regularly but there is no leakage in the light fixture now, this is what confuses me still because there's no way a water leakage problem could just get fixed on its own. Why is it not leaking now and everything seems normal? What happened differently at the time of the incident? I am just waiting to happen again so I can record it this time and call a plumber.

Anything else would help!!

That happened to me, sometimes it leaked and sometimes it didn’t. Turned out it depended how long the shower was on for..the leak didn’t show when I used it with a quick shower, but my son would have longer showers and the water would come down through the light fixture. Turned out to be the shower assembly. Replaced that, had to open it up from the back side and problem was fixed.

As a homeowner, I would have the plumber cut a hole in the drywall near the light fixture. No way to avoid that. You need to be able to visually see what's going on when someone showers and/or flushes the toilet, etc. I cannot imagine that something just "fixed itself." And I would want to know so I could get the issue fixed before it gets worse.

You mention that the leak occurred while someone was showering, but you give no further clue that you or the plumber ran the showerhead in order to recreate the leak. While a shower curtain on the outside of the bathtub or not pulled all the way closed is a possibility, it is also possible that there is a problem with the showerhead piping. Did the plumber run the showerhead?

What we know is this happened while someone was showering. And not taking a bath in the tub.

Here's the interesting part, we had a plumber come in and when he tried to re-create the problem while turning on the same tub water, now suddenly there is no leakage in the light downstairs?

Did the plumber just run water into the tub or did he run water thru the shower head?

What type of tub surround do you have? Pictures?

Even if he ran water thru the shower head, that doesn't exactly replicate someone in the shower & deflecting water every which way onto the surround material.

So far, my guesses are either it leaked at one of the shower connections--either at the faucet or the pipe connections to the shower head. Back pressure created by the shower could also indicate a faucet problem. OR, there is a leak in the surround.

Half a bucket...would that be an ice cream bucket or a 5 gallon drywall mud bucket?

One other possibility....what type of tub do you have? The material? Because a not properly installed/ supported tub...the acrylic/ plastic ones...can crack. Maybe everything is AOK when a lightweight uses the shower (for now) but leaks when a heavier person uses it?

"this bathtub has a glass sliding door"

"not leaking now and everything seems normal? What happened differently at the time of the incident?"

Still the same as a curtain, the front or back can be left open. Also the panels could have been inverted so the gap is open to the spray direction.

Do you have an access panel to the back of the tub? Can you pop out the light (say recessed remodel can or new LED remodel/wafer)?

Bored little boy,,,,,,,,,,,football,,,,,,,,,,,,,,room full of monkeys.