cnPilot E410 suddenly off9 from cnmaestro (cnm) and it happen randomly

As per topic, we have like 100 units of E410 and a few unit of EX2028-P, all APs are power up by the SW. We have 3 different sites 1 site is ok, and 2 sites are having this problem where the APs suddenly off9 from cnm, (when we remote the site we can still ping the AP). AP ip range was 10.8.32.x/22 and SW ip range is 10.8.30.x/22. All 3 sites are on different locations but we use the same AP and WLAN profile (Copy and paste) so its weird the off9 thingy happening only at these 2 sites and the 1 site never happen like this. It happen only with the APs not the SW. Would appriciate any ideas that can help with this.
Not all the AP will goes off9, its randomly pick and once it happen it will like unstable once it goes on9 it probably will goes off9 again.


same IP in the network ?
arp issue ?

we check, none. on ARP site idk, can explain more what ARP do? since we dont control their network. I dont think we set ARP on our Cambium SW either