Try make a practice session playing scale.. Play as lightly as possible. Nothing but focus on how light you can do it and still get a clear note.. Then do your lesson where you get to that problem.. As soon as the problem arises, go back to your light touch practice.. Make sure you are no getting tense in the area that the problem occurs..
I once new a fellow that would start strumming normal then get going faster the harder he play.. He would start curling into a ball get so red he would like he would explode.. Now that is tense.. or intense.. Hope you work it out..