tv connected to line in

No, the normal line in, which is analog, gives a minimum of 75ms (but can be more, depending on settings). The digital input (HDMI-ARCj gives as low as possible delay to the Sonos device as it is trying to sync with video. However, you pay that extra delay tax when you ‘group’ another Sonos device with the device receiving that signal. 

Things are operating normally. 

75 is perfectly ok, but it is several th ms. And until recently it was ok, just noticed it today.

Is it possible to use the eARC output of the TV to conect to the Amp's HDMI input?

That avoids the delay mentioned above.

I have an old amp it only has line in no hdmi input

But the point is it was always ok no delays at all until literally today

That is odd. 

I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here.

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 Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Yes, exactly, odd.

One of the many aspects I never use, I’m afraid. Apologies for misunderstanding your initial post. Odd that an update would change that for you. 

Always helps to clearly identify which Sonos you have, the Amp and Connect Amp are very different.

Filling out your profile's products list can help if you don't have it in your post.