There may be a current bug, there have been several other threads about this. You’re best bet would be to submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. They might be able to confirm that is what you’re suffering, or perhaps come up with a different explanation. 

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your Sonos system and network.

Is this while CONNECT is Grouped with other players?

If CONNECT’s LineIn delay is different from other players, Delay may have been adjusted.