I am not using any VLAN Tagging, so there is only VLAN1 the default. Yet the MX18 is showing this warning.
This device is using a DHCP IP address from VLAN 0 instead of using configured VLAN 1.
DHCP is being run by my server. I have tried setting a static on the AP, but that didn't resolve the issue. It is back in DHCP mode and passing traffic, but the warning stays and is annoying.
VLAN 0 (no such VLAN ID) should indicate "untagged" and typically generates that type of DHCP warning in Dashboard. So just out of curiosity, try this, click into that AP's page, click on the pencil next to LAN IP, and for the VLAN box, leave it blank, don't even put a "1" in there, just leave it blank and click save. Wait a few minutes and refresh the page, see if that does it. Should not have to reboot the AP, but try that too if it's not automatic.
To be sure, I just reproduced this exact issue in my home lab in just a few minutes by placing a VLAN 1 tag on an AP, got the warning, then blanked out the VLAN field, and warning goes away.