I haven't really solved the problem, but I have worked around it. When radio.delay is used to make delays that are less than 262 ms, then the crashes occur, as I said above, about once per 500 trials in about 1/3 of the nodes. When I increase the delay to be over 262 ms, then the crashing stops. I have no idea what the reason is.
I tried putting delayMicroseconds(128); in ListenModeEnd(), prior to:
writeReg(REG_OPMODE, RF_OPMODE_SEQUENCER_ON | RF_OPMODE_LISTENABORT | RF_OPMODE_STANDBY);
writeReg(REG_OPMODE, RF_OPMODE_SEQUENCER_ON | RF_OPMODE_STANDBY);
but this did not help on its own.