It seems to be related to FIR Filter from PlutoSDR options:
It will work only for bandwidth under 2Mhz.
Try to set RX filter to 10% and zoom out to see full bandwidth. You will see that only about some signal will pass (middle).
Probably TX works similar and might be important for spurious emissions or DATV.
At least, this is what I could figure it out. I hope I'm not wrong.
73,
Petronel
YO8SEP