**Fork detected!** [Block 6639]

Fork detected! They’ve detected two competing chains, forked at Block 6639. Stay wary!

I think i read somewhere that Grin nodes on different forks (with duplicate coinbase commitments) will successfully sync with each other both ending up on the same main chain.
If that is correct then there’s nothing to worry about

and… seems to have resolved in all if 3 minutes

natural forks happen all the time, old news