If you use these powerline plugs, your house is also a huge antenna.
My internet access dropped occasionally until a telcom guy found the culprit. It was a neighbor using a Devolo powerlan adapter.
So yes, don’t use these. The only useful frequency in power cables is 50 or 60 Hz.
This is probably the reason. Older element versions has video and telephony via native interfaces and coturn/turnserver for firewall hole poking.
The newer Element X uses a different infrastructure that even allows multi user conferences. You need to update your well-known server response to point it to the new infrastructure: https://github.com/element-hq/element-call