Rotting corner shower

We installed a new corner shower in our bathroom about 5 years ago. About 6 months after installation we noticed a breakdown of the wall at one of the 2 bottom corners. Over the past few years this breakdown/rot has grown and is now in both corners. The wall is deteriorating about 5" up and about 1' wide in each corner

I assume it is a dampness issue but the caulking on the inside of the shower is OK.

Can you offer any insight into this problem. Thanks you so much for any information.

R.K.

Hard to say from here.

You will have to replace it and you will see what the cause was.

If you post a pic we may be better able to tell.