Let´s consider that hypermobility is related to collagen homeostasis and metabolism disorders. The link between collagen and mast cells probably lies in the release of tryptase upon MC activation. Tryptase may cause proteolysis of the α chain of fibrinogen. See also: https://onlinelibrary.wiley.com/doi/epdf/10.1111/hae.13800
The link may start with EDS defective collagen. This would cause abnormal extracellular matrix organization needed for mast cell attachment and inactivity. Abnormal ECM would result in mast cell activation, excess MC cytokine production, inducing further inflammation in the joint. https://www.ehlers-danlos.com/pdf/2017-FINAL-AJMG-PDFs/Seneviratne_et_al-2017-American_Journal_of_Medical_Genetics_Part_C-_Seminars_in_Medical_Genetics.pdf