Wow well I too have a very similar issue been happening for a while. I noticed during a recent road trip that I would hit close on the frunk from the button inside the frunk itself, therefore I could hear the frunk close properly. As I sit in the car, I get a message saying frunk is open but no crazy flashing lights or anything like that. I then proceed to open and close the frunk again through the pilot panel and it's done.
Then I saw this happen again and again ever so often after I'd open and close the frunk during out second road trip, I took it to the Scottsdale Service Center and tried desperately to replicate it but it worked fine the 10 times I did it there.
I realized, or so I think what the issue is, but don't know if I should hit up the service center again or not. What happens is when there's enough load / luggage in the frunk such that there's even the slightest pressure being applied against the hood from the inside, the warning sounds!! Even though like I said, I can see the hood close just fine and you hear the 'soft click'. I've proceeded to take out the divider from the frunk so that there's no chance of any pressure being applied against the hood and have not seen the warning sign again. But that's all my guess at this point.
My only other theory, which is weird is it has something to do with the weight of the stuff being kept in the frunk.
The service center thought it was because we had dust or grains of sand that made the latch area dirty causing the warning to go off but I wasn't quite satisfied with that answer because it was not happening every single time. It was perhaps every 2nd or 3rd time of open / close