Where could water be coming from inside the joint between bathtub and wall tiles?
I'm afraid your shower plumbing is leaking again. Not as badly as before, but leaking none the less. From the looks of things, water getting past the tiles from showering wouldn't amount to much, and would have certainly diminished by now due to lack of use. Continued flow indicates a water source that is not dependent on showering activity.

The reason you are not seeing water on the kitchen side is because the leak is fairly small and the water found somewhere to go that has enough flow capacity such that the water does not overflow across the wall baseplate or subfloor into the kitchen side.

Bear in mind this is just my best guess. Water leaks can be difficult to trace to the source. No matter what, something is not right and needs to be corrected. Even if the source is something else, you need to get into the wall to investigate. Presumably this is easiest from the kitchen side. Would this be how the plumbing was accessed to repair the previous leak?