What router are you using?

I'm using a Motorola cable modem Wi-Fi router but since I posted this I figured out what was wrong. I have two separate bands activated, 2.4 and 5, but somehow the guest login was left on and was also set for five gigahertz. When I was logging in to my router from my phone it was logging into the guest login which shows a different Mac address and also blocks you from seeing things on the network. I turned that off and now everything is working fine.

I use three different names for each band, 2.4Ghz, 5Ghz, and guest...just to make my own life much easier. Having the same name is confusing to me. :)

ive noticed this behavior just recently.  ive always had my speakers on 2.4 and never had a problem controlling them on my 5ghz phone.   now all of a sudden, i either rarely see my speakers appear in system, they appear with questions marks, or i get ‘no sonos system found, fix it?’  icon at the top

this nevvvver happened before.  feels like something changed behind the scenes

Could be the firmware running on your router. Mine frequently updates in the background without notification, I occasionally have to log in, and check the settings. 

I’ve had the same difficulty with a cable box, and a TV set….

i have an older but rock solid archer c9.  never had any issues with the sonos app till recently.  i guess i did add some surround speakers, so i am in the app way more than usual, but im seeing so many missing speakers, then reappearing spearkers, , speakers not being found, question marks etc   likely because my phone is on 5ghz, and my speakers are 2.4.      it definitly should be a QA Test Case or something cause im likely not the only one with this kind of setup

That sounds a lot more like a duplicate IP address issue to me. Try unplugging all your Sonos devices from power, then reboot your router. Give the router two minutes to recover, then plug your Sonos devices back in to the power. 

Do you think that is the reason I see question marks like in the above pics?  They only show when I connect my phone to 5ghz.  As you can see they all appear fine when my phone is on 2.4

Not 100% sure, but doing that suggested process has no downside. Although seeing them on one channel, and not another suggests a mesh network or router issue more than duplicate IP addresses. You may want to submit diagnostics from both ways, then call Sonos Support directly to discuss it. The information that they should be able to see might help hone in on this. 

thing is there is no issue with my sonos system or network.  all my speakers work fine.   its just that they are on 2.4 while my phone is on 5ghz, so they dont show up on my phone 100% of the time.   

i swear i used to be able to see them and control them all fine on my phone for years, but all of a sudden they start not showing up, exactly like the OP is describing.

Which is why I’m suggesting contacting Sonos Support.