This has been there for a little while, but it has only just started causing problems as I aim to investigate why I’m getting so many bounces at present.
The issue seems to be that there is no link in the Email Type column and nothing behind the 
icon (red arrows):
When I click on these I get this:
Looking into the page code, the anchor tags in the HTML seems to be missing the href altogther:
I’ve got VERP configured for Mailgun, and it seems to be working well otherwise.