If you have asked teaching trainer to give the horse the day off and she has the other Pro ride him anyway? Why do you allow that?
It could be horse is tired, sour, needs a vet workup, equipment does not fit. But why do you need to tell the trainer? Problem solving is part of their job description, they should be telling you? And why did you have to post on here horse was pulling you and you needed a different bit? That is why you are paying a Pro.
It could be you, why doesn’t teaching trainer work with you on these problems? Maybe its the wrong horse for you, why has trainer not suggested this to you? Or are they more interested in the continued income stream you provide? Did this trainer sell you this horse?
Thing that bothers me most is that horse is running out and stopping with you? When (not if) you come off, you will likely be moving with some speed and end up hitting part of the fence. You could get hurt and trainer really ought not to have you jumping that horse right now. You cant miss work for avoidable injury.
There may be more to this story and we dont have trainers side. But, based on what has been shared on here, this is not the right training program for this OP and this horse at this time.
JMIO based on what has been shared, horse is working too hard too many days a week every week and needs some rest, a vet visit and likely routine maintenance to deal with age/mileage related arthritic changes in joints and possibly back. Has trainer discussed these possibilities?
One other quick thought. The behavior you have described here and on the earlier thread about the bit? Its consistent with pain related behavior which would get worse with a heavier work schedule as he is in now on. He’s trying to tell you something, listen. And, no, he wont try to tell the Pro rider because he fears discipline more then the pain.
Give it some thought. And get him off that schedule,