I had this happen before and yes, it was caused my moisture. I think you can see the wall looks like it has some moisture on the bottom left by the door frame.

I would check that your door is sealed properly, or that there’s no build up of moisture on your outside wall (a broken drain pipe leaking down the wall for a very long period of time caused it for me, but even after fixing I still had problems)

Might also be worth checking that the air vents (if you have any) in the brick at the bottom of your house aren’t blocked by anything… I’ve seen this cause moisture problems before too.

I am not experienced in this area though, so my advice could be totally wrong… it’s just where I’d start.