I will "echo" the suggestion to fly and get a PAPR. With that, you will be able to determine if the Baro Alt failure is 100%, or only part of the time.
If it is part time, are you flying in the fringe areas of ADSB ground station (GBT) coverage?
Also, when you fly, take along an iPad connected to a Stratus receiver. That will allow you to monitor all of the ADSB out parameters real time. You can access the info from the map page, select settings, scroll to bottom of menu, select Stratus, then scroll down that menu to "ownship" and tap on that. That displays all of the information about your ADS-B out, and is color coded green for good, and red for bad.