you can try wds bridge. see the FAQ here. https://www.tp-link.com/us/faq-1385.html

i contact tp-link before and they told me if we login remotely to this router, those iteams are not supported, which means they are only for local access. but can't find any document saying this.

can you access other local network fine? vpn ip address is in the same subnet as plug? have you enabled vpn to internet on the vpn router? maybe you can ask for some suggestion from VPN router...

i think sunset/sunrise won't work as the plug need to communicate with cloud to get the sunset/sunrise time.

how about the lights on the adapter now? do you mean the firmware update bricked the adapters?

what is the hardware version of your device? like v1 or v2 or v3 etc.