I've noticed, randomly, I can't figure out a pattern...but if I try send a voice message on telegram, sometimes it's muted. There's no notification except once the voice message is sent, it's blank.
To undo this, I have to make a normal phone call and the mute button is activated. By unmuting on a telephone call, it then sorts it out for everything.
The microphone access toggle is not touched during all of this and still shows as "mic access available"