Your not alone! I have an XT camera which is at least 3yrs old. That still works with my sync module mk1 but my recent 6 month old Blink doorbell doesn't show clips now because they want a subscription whereas before it records anything.
So, I stuck a storage usb in the sync module expecting it to work and show recordings but that didn't work. Turns out after some digging on the 'net it is just a supply out to power another device.
Today, I've ordered a sync 2 module..... still don't know if that'll work ok. Hopefully it'll work as it should with it storage on usb stick.
So if your using an old sync module you might need to upgrade.