Same here. I emailed both the developer and the researcher at UCSF. I uninstalled and reinstalled the app and no change. Should hear back in a day or two.
I had the same issue and found that it is related to the current date on the phone. If the date is past December 31th 2018, the app doesn't work. Change system date manually to prior to that date and the app works again! I hope this limitation is in the "My BP Lab" app and not in OS itself...