Best as I have interpreted what I have read and seen with my own eyes,,,
a. if the plane momentarily loses the signal the PCM rx just holds the last good input and you never even see it.
b. If the rx loses the signal for about 6 seconds the controls go to the "failsafe" mode that you setup in the transmitter. I set my failsafe to idle and straight level flight. Lots of guys set failsafe to min throttle, and basically a snap-roll input so that if the signal is lost the plane just balls up and falls straight down. But remember this failsafe doesnt happen unless several seconds of signal loss elapse, if its just a few seconds the controls just hold their position where an FM rx will be jumping all over the place from the false signal.

From what I understand a PCM signal is basically a coded signal. The rx gets the signal from the transmitter in code, the rx decodes the signal and sends the signal to the servos. So if the signal coming in is on the right frequency but isnt the right code the rx ignores it and continues with the last good code. Dual conversion Futaba Rxs do the same thing but its more than 1 "code". That may not be the best technical description but its the general idea.

A plane will crash with a glitch way less than 5-6 seconds so an FM receiver that loses singal is doomed where a pcm may just overshoot a little. From what I understand,, seldom does real interference last that long so the PCM receiver maintains the last good signal and the pilot never even sees it. All I can tell you is that I havent ever seen or heard of a PCM rx lockout being the cause of a crash. Maybe PCM rx failure but few if any crashes due to interference.