I had that recently too. The joint had come loose and suddenly stood up. We also had no water damage. At least, we didn't notice anything. I then got a special adhesive and smeared it into the joint. So far it holds.
Moisture can get in quickly. Especially during the wet season, moisture is often brought into the house on the shoes. Therefore, the joint, which was just under 3mm, was welded. So now it is definitely sealed. We are not bothered that this is now visible.
Yes, I had this problem too. No one could explain how this joint swelled. Everything was dry and there was no water exposure. It could only have come from wet shoes. I then welded this joint and since then everything has been TOP.