When your track signal is good but maybe not perfect, 1 or 2 pieces of offending equipment parked in the right spot can tip the scale and lower the signal.
I can usually pull my Lionel tank cars w/ sound around without issue. Every once in awhile they have to be removed from a train if there's an issue. I should add chokes but I haven't.
It would be nice if somehow the app could tell us the exact issue it is seeing. We have to search for it.