When I arrived at the station on the 18:34 from London Bridge, I noticed that all the gates at Perry Vale were closed and unmanned. As a result there were a few people unable to exit the station. I popped into the main station to inform them, the guy on the barriers seemed to take it very seriously and hopefully the gates were opened shortly after.
Hopefully this was just a single incident of an oversight but if you see the gates closed and unmanned please tell the station staff. There should be somebody at the station (not necessarily on the Perry Vale side) at all times trains are running. And if you do get stuck I think there is an emergency gate opening button to the left of the gates as you exit.