I am sorry you had this experience. I am in a DOD long Covid study too. Everyone puts on a mask when I am there without me asking, but they are surgical masks. I’m always wearing a N95 mask. On my first appointment the intake person was unwell and left early which concerned me a bit. The staff are very welcoming and accommodating but as you observe they would be better serve their study participants by always masking whenever in the office and with N95 masks and having air purifiers in all the rooms on all the time. It would really put me more at ease if so!