Hello @JamesWhite
The train can stop in the tunnel due to special events such as waiting for another train or construction work on the line. However, we cannot say how often the train stops in the tunnel.
If you have problems during the trip pleas contact the personal on the train.
The ride through the Lötschberg tunnel takes 15 minutes and through the Simplon tunnel 20 minutes.
I wish you a nice day.
Kind regards.
GiorgiaB