The most usual reason trainings are not synced between two co-riders is that the horse has not been chosen on the training. So, make sure the other rider have picked the horse on the training that is missing and that you have chosen that horse in the view you are in.
If the trainings still are not syncing then try to close and open the app while connected to wifi, repeat this process a couple of times. This makes sure it syncs all trainings that is stored locally.
