Are you using 802.1x authentication on those ports?
For the last two weeks, I've had a number of computers that started to end up on the guest VLANs despite successfully authenticating. It takes a shutdown-wait-startup cycle or a port bounce to correct that (just a reboot wasn't working, needs to actually turn off).
I did update the firmware on our switches, but in an attempt to fix the problem, not before it started.
This seems to only be happening to new computers that have upgraded to win 10 1903 and have discrete TPM. I suspected new/updated "virtualization based security" features in windows could be to blame, but so far turning them off hasn't seemed to help.
I'm working with meraki support, just sent them a ton of pcaps last night.