Sort of sounds like an issue with the IP address that these 'cameras' obtain when everything is working well.
When you het a power cut, and power is restored, it can take the SH3 a good amount of time to boot up, until that has had sufficient time the DHCP server included in the SH3 won't be signing IP addresses from its pool, meaning connected devices (wired or wireless) won't be getting an assigned IP address. Therefore won't be visible on the network or have access to internet traffic.
Putting aside why you are getting frequent power cuts; when this fault scenario happens, do other devices on you network work and can access the internet served by the SH3? Is it just the 'cameras' that fail to access the network/internet? If so, what if you reboot just the 'cameras' without rebooting the SH3? Does this then allow them to work? If they do work after a reboot of those devices it suggests that the time these 'cameras' look for an IP address to when they get an IP address from the router is marginal.
You could either look to delay the boot up of these cameras, or look to install a DHCP server yourself like a Raspberry Pi running say pi-hole and setup the SH3 without a DHCP but wired to the pi-hole. Thats was I use reliably on my home setup.
Hope this might give you some ideas to investigate. Sorry if its too techie as a response.
