The ‘monitor host’ option in cnPilot E series can be used to solve this issue:
https://community.cambiumnetworks.com/t5/cnPilot-E-Series-Enterprise-APs/WLAN-Up-Down-depending-on-reachability-of-a-critical-network/td-p/59181
it is not automatic monitoring of internet as-such but you can specify your gateway/router or some public IP for the AP to periodically poll to determine internet connectivity