Interesting. Just out of curiosity, have you tried something like this?

Leaving everything pretty much as-is, create a short sub-routine and use any available I/O-pin to just blink an LED in an endless loop.

Leave the RF receiver connected, send data with your transmitter just like you were before, but on the receiver side just jump around the SERIN2 routine directly to the LED blinking loop.

Inbound data will still be banging on the serial input pin, and creating in-circuit noise.

Does it lock-up or hang in the LED blink loop requiring the hard reset on /MCLR?

Now try the same thing, but without the the receiver in the circuit. Does it hang in the LED blink loop after removing the RF receiver?