I had that problem on my first note and none of the workarounds helped, not even factory reset, had to send it in for warranty repair but I suspect that they just reflashed the software, problem haven't reappeared yet but it's not my daily runner as I bought another one, couldn't wait 10-12 days on top of already waiting 5 days for them to sort out picking it up
you can try and clear data in usb settings, also clear cache in recovery, if it doesn't work you can still charge the phone either wireless or by plugging in the just as you switch it on, a pain having to reboot every time you want to charge though and it will be regular instead of fast charging.
I rinse my phone off sometimes and that message pops up, as it should. You don't want to charge your phone with water in the port. It will go away after it actually drys. Sometimes it takes a little while. The good news is that you can still wirelessly charge it if you really need a charge while you wait. I think the longest I have had it stay on was about an hour. Seemed a little long, but I assume it was still sensing moisture because it did go off on it's own without me rebooting or doing anything.
Yeah it'll go away..... Eventually. Even after a few hours and you're convinced it's bone dry it'll still detect moisture. Just be patient and don't be tempted to blow a hairdryer into the port to speed it up. That could force moisture into the phone and you don't want that. Having a wireless charging pad in the meantime will at least let you charge it when a USB plug won't.
glad it is sorted, just pay attention to it coming back, mine got that message without being near any moisture, it went away, came back and then got progressively worse until it was all the time