invisible subpanel

I have a missing subpanel after upgrading to v12 Enterprise on Site, and it's still missing on v14 Enterprise on Site

When I look at the list of subpanels I can see a bigger gap where the missing subpanel should be.

Looking at the source code for the page, I can see that the subpanel is there but clearly something is missing as the div that should contain the header , panel top etc is empty.

I tried to do some digging but I really don't know what is happening.

Any ideas?

thanks,

FrancescaS