Not sure if this issue I've experienced is directly related to this RC, but..
Our MX68CW WAN connection configured for DHCP returns FAILED status even though it picks up correct DHCP config and switchport status on the uplink switch correctly shows A-FULL/A-1000. Multiple reboots does not bring the connect online.
I had to rollback firmware to 18.211.5.2 and the issue resolved after rollback + one additional reboot.
Luckily there is cellular backup at this site (in Darwin, 4 hour flight from Sydney Australia) which provided Meraki Dashboard access (even though the AutoVPN does not work with the cellular backup as everyone is aware).