I'm not sure if understand your problem correctly but maybe following might help:
If you have configured native VLAN for port on MX or switch port where switch or AP is connected and using VLAN tagging on IP configuration then you might encounter errors on the switch or AP.
Try using only trunk port without native VLAN or remove VLAN from IP configuration on switch or AP.
Check where is your mismatch, like : if you add the MX84 the Cisco OpenDNS address - 18.104.22.168 and 22.214.171.124 / not mandatory but i believe its preferred when specially you using Cisco Meraki AMP - then use the same DNS address down in the stack with every device.
Is the mismatch on the MX or could it be on the Switch and AP's themselves? If they have static IP's you would have added a DNS entry as well. Just a thought on the matter.