I have one suggestion... Did you try a bulb?
How is the dcs signal on the other parts of the layout?
You may have to determine whether the channel is putting out a decent signal by using a small test track with one engine. ..Should be able to get a perfect ten.
I've also had dcs still 02 with over 8 scale miles of track and the layout runs really well. Yes we have an version L in there someplace but I can tell the difference from the L or original G. Both are working. Magic bulbs on the terminal boards. You do know the odd TMCC engine can destroy the dcs signal?
do have the reds going to the center rail. Blacks to the outside.
Is it possible you may have a loose transceiver board in the remote or remote.? (tether)
Some of the runs from the tiu to terminal strips are around 30 to 40 feet.