For me, on Windows, the address bar autocomplete drop-down just stays there indefinitely. I would have to press the Esc key to hide it.

Where is your mouse cursor starting its journey toward the suggestion you want to click? I'm wondering if it might be passing over something that causes this problem.

Forgot to say Mac. I'm now trying to replicate it to time how long it stays and its not doing the same thing. In fact its staying there until dismissed which is weird. Its never done that before. Perhaps it repairs itself!

I'm not going mad as the reason I posted is that it happened the thousandth time a few mins ago. I might have to test it more to see where the mouse focus is when it doesn't work, or train myself to use the down arrow instead.