Oh how odd, this fixed it for me as well.
With the dev tools open, just clicking the “standard” link didn’t work, but Ctrl clicking to open in a new tab did.
I use the “start from last time” setting and my gmail tab is never closed.
I wonder if that had something to do with it.
Very, very odd! Thanks @AgentStarling
Edit - just to note, the original tab still won’t load normal HTML, but the new one loads it fine every time.