I'm reversing a USB protocol of a device. It's based on USB HID reads, and writes. The protocol always has an 0xAA after the header, and every occurrence of 0xAA in the payload is doubled. After some time I figured out that this could be a synchronisation symbol. The company who built this device also has similar devices that support Bluetooth LE. The protocol is incompatible, but clearly shares similarities, especially it also has those 0xAAs.
Is it necessary to have synchronisation symbols inside of USB, or BLE packets? This looks very weird to me.