So I know the answer I think, but I thought I'd check.
Every plugin module I have tried has issues with turning off randomly at some point or another. It might be once every six months but it happens. I need power mon only, for an appliance or two AND for my individual systems in a server rack. I have disabled the on/off entities in HASS but it still happens and within zigbee and z-wave add-ons there seems to be no way to disable the actual functionality. I've got models from tons of vendors, and it's been a problem with all of them eventually. Where appropriate they are set to "Power on when power restored" in case of brownouts and such but it will happen when power is stable and clean. All the models I have are like 15amps and 1800 watts and do not seem to be tripping protection circuitry.
Is there a NON on/off plugin module? I speak all the languages, zigbee, zwave, matter, thread, wifi, HA smoke signals 2.0, clapper, X10, etc.
An alternative is clamps, which is not in the electrical loop, but sits outside and monitors there.
The drawback is that you can only have one phase in a clamp, so you might have to strip a section of the power cable to put on the clamp.
The clamp solution is especially used with high power setups, because they do not have to handle the actual power in this solution.
This is just one example. Search for one that fits your purpose and/or ask on the forum.
Honestly, I use a mix of Zigbee relays, and every outlet in my home is a TP-Link smart outlet with power monitoring. Even without internet, they still work locally over wifi (i know this because a mouse but my fiber optics cord on my modem, was a very upsetting day).
The real issue usually isn’t the protocol. It’s whether you properly built out the network. Think of it like Verizon building cell coverage, except you’re doing it inside your home.
This matters even more for smart outlets/smart devices inside walls and recepticles because many are installed in metal boxes, which can weaken the signal. That’s why I use Wi-Fi repeaters and Zigbee routing devices throughout the house. My Zigbee DIN rail monitors also act as routers, so they help strengthen the mesh.
What is plugin module?
Shelly has good variety of power monitoring devices without relay.
Atomtech has power monitor plugs without relay (never tried personally).