Can anyone diagnose this problem?

This is a shot in the dark, I had similar problems on my Legacy layout years ago. Is the wall outlet, that Legacy and the transformers are plugged into, properly grounded? I had this almost exact symptoms and out of desperation I plugged an outlet tester into it and discovered the ground pin was open. Rust had built up on the mounting screws to the conduit. Replaced the outlet and never had signal loss again.

Try running them independently and see if it's just one engine causing the issue.

My guess is something mechanical from the look of the video.

Thanks John! I will run a test and see what happens.

Interesting idea Ariezman... I will look into that 

Timing is everything. Just last night a fellow TMB club member had the same pair of engines, We tried programming the engines with the same number and later with different numbers. When either engine was on the track ALONE it worked as expected.  When we had both units on the track together, and of course we had them in position but not coupled, only the lead unit moved the second engine just stood still (&*^^%$^&.  Seems to be an issue with these units.  Any help here would certainly be appreciated. My fellow clubber, is likely sending these back to Lionel for servicing.