Hmmm. So it’s not likely to be an issue with duplicate IPs, as that process would have cleared that up, at least until the next software update.
I’ll admit I’ve never heard of an icotera router before, but generally speaking, use of 2.4Ghz vs 5Ghz shouldn’t make a difference. I tend to stay with 2.4Ghz for superior distance and penetration, there just is no need for the extra bandwidth of 5Ghz for Sonos. Nice to have the option, just no benefits.
So my thoughts lean toward wifi interference . Although I’m not convinced. I think your best bet at this point is to submit a system diagnostic within 10 minutes of experiencing this problem, while your system is ‘connected, 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.
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.