I don't know if this is a known glitch or not. I managed to put the game into a state where radio calls no longer functioned. I don't exactly know how I got this to happen but I think I despawned a gaurd trying to radio to CP. Once triggerd the glitch persists trough restarting the mission or going to the title screen (I didn't test reload checkpoint). Closing the game does fix it. I messed around with it a bit until I tried closing the game. From this I figured out a few things:

1. -Kaz cannot talk to you except for cutscenes and you cannot call him.
2. -Gaurds cannot enter the Alert Phase when noticing something suspicious.
3. -If you call a chopper to a dangerous location, CP cannot order the gaurds to shoot at it. They'll only start shooting once they see it themselves. Morpho also cannot talk to you.

There are things I didn't test before trying to close the game:

1. -If CP can request a gaurd to check on a broken camera/power supply.
2. -If gaurds still automatically enter Alert Phase on Destroy The AA's mission.
3. -If gaurds can request backup during combat when they suffer numerous losses.
4. -If tapes still work.
5. -Other things I'm not thinking of.

I’ve had this happen to me as well. I don’t think it benefits nor saves time on IL or full game speedruns though. I had this glitch happen during the helicopter mission and the mission had an issue progressing further because of it.

That's an interesting side effect to be sure. It would be nice if we had some idea of what triggers it to occur. I hope I have it happen to me again since I really want to experiment more with it for fun.