I've used the Sonos arc, sub mini, and one SLs for over a year and I've never had any issues.

Last week I decided to get two era 300s to replace my one SLs because I watch a lot of Atmos content.

After I installed the era 300s, the whole system's sound cuts out randomly, and does not come back.

I'll be watching a movie on say Disney+ and the sound will just cut out, not just in the 300s but all of the speakers, and the tv will continue to play the movie.

All speakers are connected via wifi, I have rebooted my router and unplugged everything and plugged in the router, then tv, then the arc and each speaker to make sure they're all connected to the same network (2.4ghz).

The Sonos arc is connected to my LG G2 77 tv via the hdmi cable that it came with to the tvs eARC port. 

One way I've found to get the sound back, as it doesn't ever come back on its own, is I go into my TV's sound settings - > click on digital sound output - > change the sound from pass through to auto, and then back to pass through and the sound comes back on.

This is obviously a pretty easy way to get the sound back on, much easier than when I'd turn my TV and speakers off, unplug them and plug them back in lol. 

But the problem remains, and since I never had any issues with the one SLs, the era 300s seem to be the issue. 

My system: 

LG G2 77" (watch using native apps)

Sonos arc 

Sonos sub mini 

Sonos era 300s surround 

If anyone has any ideas I'd love to try them, I've been told on reddit to buy a new wifi router, but I spent 200 bucks on my current one, it's been cleared by Sonos to work, but like I said if people think it's the router I'm more than happy to try and replace it.