Funny you ask. I was running a sesson in 111951 yesterday and suddenly sound on the two loco's on the head of my train dropped out. There was a "buzzing" background type noise. Then I also noticed that the loco's fans quit spinning and smoke died. I quit session and started the latest saved Driver session and things were still broke. I went to Surveyor, reset Session, still broke.
Trashed saved Driver session. Started Driver from new orignal session and all was OK. I did't take the time to do any debugging or try to break again. As I've ran this saved session repeatedly over and over and had no problems so I figured it was so random I wouldn't be able to reproduce.
Are your issues with any particular route/session or Loco and was the big gigantous "double" crane around???