segments of track strangely losing audio

For instance one segment of a vocal track suddenly stops producing audio, even though it’s there and you can see it you can even go into vari audio and edit it but it will not play with the track. If you edit it by changing the length muting it, etc the segment completely disappears.
This started on a vocal track now it seems to have gone to a portion of my drum tracks…anyone know what’s going on?