I too carry the same 3 diagnosis as you. I also take a beta blocker ( bisoprolol 5mg every day)
Beta Blockers trigger degranulation of the mast cell and also plays a role in the pathway of epi release when needed for anaphylxis. Sometimes Glucagon is needed as well as epi if an allergic reaction becomes bad and you are on a beta blocker. Its actually much more complicated than that but ill leave it at that.
AS well as the EDS I have hyper pots and have trouble with epi/nor epi surges and wild BP and heart rate swings. I have tried a plethora of meds, Calcium channel blockers, clonidine, and 5 other beta blockers before we settled on the bisoprolol. The docs I saw at mayo and my dysautnomia doc that the benefits outweighed the risk. I am for the most part very well heart rate and BP controlled and the surges are few and far between now. I know some of the folks I have seen want me off the beta blocker for the MCAS but at this point I am staying on the little bit.
I have so many other things going on ( neck pain, head aches,multiple dislocations, sleep issues, horrible GI issues) currently that the beta blocker issue is one I am leaving alone.
Hope that helped