Sometimes it can be inactivity that can cause the diaphragm to become inactive. I had this problem myself from heart failure 💔 problems and was at a place where they had an Austrian trained physiotherapist they had me see as I could not take deep breaths anymore. He worked on my diaphragm for 1 session over a year ago and it solved the problem even before I left the office! Perhaps if you find someone who can do diaphragm work it may help. I had never heard of this kind of deep tissue work before. Take care.