This is not just Parkchester, though that stop is one of the worse ones because it's a major transfer point. I've seen the same dead-reader problem on the Q44 near Flushing-Main and over by the Bronx Zoo. It tends to happen most on the older Nova buses. The rear readers are basically mini terminals that need a data connection to settle the tap. When the bus drops signal around the Parkchester underpass or the big apartment blocks, the reader either blinks red or goes blank while it reboots. It's not that you're tapping wrong.
The issue is that all-door boarding signs are still up, so people naturally pile in the back. If the reader is down, the official move is front-door boarding, but that only works if the driver actually notices the dead reader and uses the intercom. In my experience, some drivers catch it and some don't. When the back doors open for boarding anyway, you're stuck in a gray area: you waited, you tried to pay, and the machine failed, but fare enforcement isn't always going to care about your story.
If you can, take a quick photo or short video of the dead reader before boarding. Then board in front. Don't keep tapping the rear reader over and over. I've seen people do that and end up with duplicate pending charges on their OMNY account. Once is enough to know it's down.
The BusTime app sometimes shows service notes for SBS readers, but it's not reliable at this stop. Until the MTA swaps the older buses or fixes the signal issue, front-door boarding is the safer play. The Parkchester stop is especially rough because the Bx4A and Bx36 transfers create a big crowd at the back door, and people don't read the tiny "front door if reader is out" signs.