Check the utilization of the EAPs just before the issue occurs. Also, does this disconnect only happen with wireless devices? What happens if you plug in a device directly via ethernet cable? Does it...

@Javito Do all devices lose connection at the same time? Also, is the issue only with Wi-Fi devices? Would it be possible to factory reset the EAPs and see if the issue persists in Standalone mode?...

@c-ta As GRL said, please use the custom IP to specify your LANs.

@c-ta When setting up the Site-to-Site VPN between the routers, did you ensure to specify the VPN subnet as well as the LAN subnet when it comes to Local Networks? Please see the screenshot as an...

@c-ta From a PC behind the ER7412-M2, can you ping the cameras? Just to show that the Site to Site VPN is functioning between the routers.