I know this won't help the OP (since this was 4 months ago), but for anyone else who is using a filter:
Your gateway HAS to be plugged in downstream of the filter, so it is on the same leg as the MTU.
In the picture above, the OP shows a dedicated breaker powering the MTU through a filter, and the gateway is plugged in somewhere else.
It was quite a bit more than 4 months ago and No that isn't what I said in the description and it is not what the photo shows.
Perhaps take a bit of time to re-read the post again and look closer at the photo.
The text is VERY clear how things are wired up. 3 of the 4 bullets that talk about wiring have a line stating the black wires of the MTU, Romax and filter are all wired together.
If you look at the panel photo, you can see the black wire from the romax dropping down in front of the left breakers and passing by where the red dot for the "Break with UPS" is dropping down to connect the filter where the MTU is connected.
The MTU, and the dedicated outlet that has the gateway plugged into it are both on the same side of the TED inline filter.
The inline filter is in between the dedicated breaker and both the dedicated outlet and the MTU.
The black wires from the dedicated outlet and the MTU are literally in the same wiring nut.
So the gateway and the MTU are connected to each other on the same side of the filter just a few feet apart.
Your drawing is exactly the same as what I described and showed in the photo other than I'm not using a plug in filter in the dedicated outlet where the gateway is plugged in.
In the end, after a few frustrating calls to tech support and actually getting into an argument with the RMA person over how they handle their MTU RMA/returns/refurbishments, I abandoned trying to get the MTU looked at by them. I was able to acquire (BUY) another gateway from a 3rd party for a lower cost.
Against all of what tech support said and predicted, it did turn out to be a bad gateway. I could literally swap out gateways on the EXACT same plug and the 2nd gateway would work while the first would fail. Both were configured exactly the same way.
Once I had the new/good gateway, everything worked as it is supposed to work including without needing the TED inline filter.
I could place the gateway in my office even when the UPS was on the same circuit.
The USP is plugged into a surge protector and the surge protector filters out all the noise from the UPS so I can have the gateway and the UPS on the same circuit in my office.
All is well and has been working for for a while now. I should have done a follow up explaining that the issue was a bad gateway.
I have no idea if the updated f/w on the first gateway made it go deaf from MTU transmissions but the working/2nd gateway uses these revisions:
Gateway Version: 1.0.400
Daughter Board Version: 1.0.88
Foot Prints: 1.0.223
MTU Version: 1.0.57
And I did not update it to the latest f/w.
--- bill