The "standard faceplate" that you have the dangly filter plugged into is the master faceplate. The socket that faceplate plugs into is an NTE5(A) master. Do you think the fancy one is the master?
Did the engineer fit the whole assembly your dangly filter is plugged into?
You now add to the questions

. Does either the fancy one or the bedroom one work with that NTE5A faceplate unplugged, as in your photo.
The wire I asked you to remove is the ring/bell wire, which in your installation isn't needed, but almost always causes a lot of interference with broadband. But it might be needed by the next occupant (unlikely but possible), which is why I said not to cut it. It may need reconnection after you have left.
Asking you to check whether either of the other two sockets work at all with the NTE5A faceplate unplugged is checking for "star wiring". Star wiring can be even more damaging to broadband than the ring wire.
Everyone else here would want you to do what I ask if they were talking to you. Though a few may know the connector numbers in the fancy socket. If you want help you need to supply the information asked for and do the tests requested. So far you haven't supplied all the photos ukhardy and I asked for and seem to be trying to second-guess us.
The only guaranteed thing you need to do is remove the wire I said to. That might help a lot. But it might not, if you have star wiring or some other wire colours are what we call "split pairs". Which is why I want to know the colours in each pin number of the fancy and bedroom sockets. And how you connect the NTE5a to the fancy.
Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
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