Inspected a condo corner unit. as walked up to the door came to my first receptacle opened it saw smoke stain it was a GFCI stuck the tester in it. It wouldn’t trip, but would trip with its own test button. This same receptacle is in line with the patio’s none GFCI. When testing the patio’s receptacle it would trip the GFCI at the front door properly. Inside the condo there was a number of GFCI’s, only one in one of the bathrooms would trip properly. All would trip with their own trip test buttons. IN the Kitchen no GFCI’s one receptacle showed an open neutral. All other receptacles showed they were wired correct.
Any good reasons as to why?
Thank You in advance