Submit a diagnostic within a few minutes of this happens and then contact Sonos support with the number it gives you.

Thank you. I will give it a try,

Sonos support told me to try wiring the sub instead of the amp:connect. That has solved the problem.

If this comes back, just be aware there is an issue with connect amps cutting out, see here https://en.community.sonos.com/components-and-architectural-228999/sonos-is-forcing-people-to-buy-new-hardware-as-they-ve-broken-the-connect-amp-and-they-refuse-to-fix-it-6888610/index3.html?postid=16698137#post16698137

The cutting out did stop for a couple of weeks but has now come back. Sonos support has told me that there is an issue with the memory on Connect Amp. So my problem is not solved.

Other folks have reverted their Sonos to the S1 software and seen a reduction in the problem.

https://support.sonos.com/en-us/article/downgrade-a-sonos-product-from-s2-to-s1

We have only Play 1, Sub Gen 2, and Gen2 connect. We have been running S2 since it arrived. This dropping out problem was a creeping issue for us. At first the Play1’s would fade in and out as well as the Sub. I thought it was a wireless network issue. Then, I recently purchased a new amp (Arcam sa20) which is what is Toslink connected to the Connect (which is ethernet hardwired in to my network). The dropouts were severe there (with Connect) and I originally was thinking that my new amp was broken. Then I used this forum posts to realize it was a common issue and realized that S2 on older hardware was the source of the dropouts in both the Connect and Play1’s. Since all of my Sonos kit supports S1, I did the downgrade and sure enough, it solved the problem.

The S1 kernel is smaller, so if a particular device is running up against space issues with bad memory, it makes sense that freeing up additional space will help. 

In another thread there was speculation suggesting a memory leak. In this scenario a unit with smaller memory would get hit first.