Guess what I found out: The speakers seem to be connected to my wifes spotify account! When I switch accounts on my android phone to hers all speakers are shown on her account. On my own account I see no speakers at all! Please fix this spotify/yamaha!!!
Tried everything reinstall relogin etc... My work around was:
To login spotify with my accout on my desktop computer which is in same network, start spotify. On my desktop my account finds the speakers. And after that my account on android phone finds the speakers as well! It is a really weird and annoying work around because it is no comfort at all to do that every time. Without my desktop computer my account sees no speakers.
I was in the very same situation, my yas 306 soundbar and 010 speaker suddenly disappeared from my phone (witha Android oreo) a while ago. Again. And this time I couldn't find any solution. I tried with all the network hints I founded but they didn't work. Then I read your post, but not with the due attention. Lukily by chance the same day I opened spotify connect in the car back home from work and it asked me if I wanted to keep listening music on my work desktop or on my mobile. I said, what? I'm not on wifi anymore. And so in the end I connected the dots.
The next day I first disconnected from my desktop spotify app at work (on which no other deviced where listed by the way) and back home I downloaded and logged in into the desktop app connected on my home wifi. And then after some minutes magically both the devices appeared. But still not recognized by my mobile. So I cleared mobile spotify cache and to be fully sure disinstalled and reinstalled again spotify from my mobile and after a while bingo! I had back my devices.
So basically spotify connect messes up when has to deal with more than one wifi network or more than one user account. In my case I can't track down if I changed anything at home or at work that caused the issue. I just remember that spotify started stop playing randomly with no reason while listening a playlist. It happened few times and the last time it happened my devices had disappeared. I was going mad so again thanks :) I second the request, please fix it.