I have a shower on the 2nd floor. Can this shower pan leak when there is no evidence of water or moisture on the ceilings or anything downstairs, there is no sign of a leak around the wall or tile of the shower or any other adjacent walls? A plumber says he used an air plug that confirmed that there was a leak. The shower continues to be used. Is there any possibility of a shower pan leak?

I have a shower on the 2nd floor. Can this shower pan leak when there is no evidence of water or moisture on the ceilings or anything downstairs, there is no sign of a leak around the wall or tile of the shower or any other adjacent walls? A plumber says he used an air plug that confirmed that there was a leak. The shower continues to be used. Is there any possibility of a shower pan leak?

Shower pans can leak, but if you have no evidence of leaking water, how did this question arise?

There was water on the floor after the shower was used but it was only outside the shower door. There is no sign of water damage after this water is mopped up.

It can leak air but not be active under normal ciucumstances water. Also, you can have a very small leak that travels on the rafters and floor boards that never amounts to more than can evaporate. Have you closely inspected the current pan for cracks in the grout or at the drain connections. All pans will someday fail.

"A plumber says he used an air plug that confirmed that there was a leak."
If a leak was detected by the plumber why didn't he repair it?

"There was water on the floor after the shower was used but it was only outside the shower door. There is no sign of water damage after this water is mopped up."

Sounds like just a regular puddle that you get when you step outside the shower.
Besides with a pan leak it doesn't show up in front of the shower door.
It doesn't sound like you have too much to concern yourself with. Good luck, Tpom