Weird DCS signal loss

Just a thought here, but since the RailKing's are slightly smaller, could it be a small dead spot in the track?  The Premier's pickup rollers might be just enough further apart to span it, but the RK's don't quite make it across?

I don't have much Legacy and no TMCC, but I'm guessing they are all a bit larger also?

The Premiers are NYC 4-4-0s and the Rail Kings are a NYC 0-8-0 and a RS-1.

The TMCC is a NYC S-1 and the Legacy is a F3 AA set.

Any Legacy engines near by?  They have been known to cause signal issues with DCS.

We know proto2 and 3  engines  carry on with the last command given so it's definitely a signal problem unless the engine are stopping or losing power.

Have you run a track signal test and how much track is involved  in the problem area... could be an easy fix

Yes, but only the Rail King locos I mentioned seem to be affected.

Odd that the 2 Premiers are not.

Also, the 2 Premiers are older, bought in 2004/5.

Whereas the 2 Rail Kings are recent purchases from much newer catalogs.

The RS-3 being the most recent PS 3.0 loco.

DCS signal problems can also arise with some of the older TMCC engines. And it effects different engines differently. You might want to remove any TMCC engines or Legacy engines to see if they may be contributing factors. If they are, it has been recommended to add a choke to the TMCC engine. Here is a post describing that particular problem.

I had the problem on mine and it was frustrating to figure out so I am talking with experience. I have the chokes to install in the engines, but have not done so yet.

Rick