Check the bedding and the torque on the action screws. A slightly loose or improperly torqued action screw can cause stringing. I had a Ruger which uses pressure on the barrel that was stringing. I had it bedded, action screws torqued and the barrel floated which stopped the stringing. Go up in small increments on the torque until you get to the proper setting. Remington should provide you with the proper settings.
I would slug the bore. The bore is most likely under sized or has a tight spot. This causes a higher pressure when cold throwing high. A very small amount of linal expansion allows the barrel to correct. I would try pushing a tight patch down the barrel feeling for a tight spot. The other problem could be set in the barrel from correction bending at the factory. I would return to the maker.
There are a lot of possibilities here. Depending on your cleaning routine it could be the amount of fouling in your barrel, i.e. it gets more fouling and then shoots better? It could also be the load you're shooting? Some loads shoot better with a cold bore and some with a warm bore.
One other thing is to check your barrel while its hot make sure that it is still free floating. The expansion from heat could be causing it to touch a pressure point that is stabilizing it rather than throwing it further off?