In general, a ’line in’ signal, while being sent to all other speakers, requires a larger amount of bandwidth. It’s more than likely you’re running into a small amount of wifi interference ! Just enough to bother the line in bandwidth usage, but not so much as to bother normal streaming. 

However, beyond reading the linked FAQ and implementing as many of those potential solutions, I would also recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution. Sometimes, a simple verbal explanation can’t match hard data.

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.

Thanks Bruce..  Now that you mention it, I had recently disabled my old modem/router combo from my ISP and switched to a Mesh Wifi router.  I did this as the carriers modem/router wasn’t capable of handling more than a fixed number of appliances (IP’s), maybe 20 or so before it started to kick appliances off the network (I of course never knew this and had to learn the hard way).  When I added mesh the goal was to increase the # of IP’s the router was capable of handling as I have installed 25+ smart light switches / plugs recently, all connected to the mesh routers 2.4GHZ signal, which happens to be the same signal used by Sonos.  Prior to installing those smart light switches/plugs I had already converted to Mesh and all was good on Sonos at that time, so now here I am again with the potential for over crowding or interference, ufff..  Who knows, it could be something completely different but I think your sense of the issue would appear to in line with recent events on the network.  I will submit a diagnostic and place a call, thanks for the advice!  Matt

Note that depending on what mesh you’re using, there could be various issues, from auto channel hopping, to split subnets, etc. I tend to recommend that if you use a mesh network, you’re better off using SonosNet (wired mode) for Sonos, but there are always individual circumstance, and one ‘easy’ answer doesn’t cover all situations. Which is why I often recommend the route of a diagnostic and calling in, since there is likely to be hard information that might normally take days or weeks of back and forth in these forums to uncover, much less understand. I wish you luck!