What is happening here?!

i’m using asterisk an is running well
but sometimes when i’m talking with someone via PSTN (Zap/3) during the call sometimes i can’t hear anything and some seconds after that the audio come again and i can keep talking…

i test this many times calling …and is just a few times me asterisk do that, not always but… Exist a way to prevent that?
I the CLI anything rare happened it looks like normal.

Increse the level of Verbose and debug and see the console and post it