That looks like water ingress between the panel and the tile.
If ingress is getting down between the joint, it would not necessarily mean poor waterproofing. The swelling would need to…

Looks to me, to be more corrosion of the screen/frame than any leaking.

Couple of close up pics of what I have.

I have Gal hoists, no affect there.
I just chipped dark area away, and I basically get a 3mm deep strip, and a single hole through about 50mm.
I was thinking of…

Thanks for reply. Looks like there is a small section of wood rot up under the wall.
Cut out 200mm etc and replace?

I had a leak under the tiles in my shower.
After pulling up all floor tiles, i found a few small patches of timber rot in the board base.
After removing all…