Try rebooting your router and phone.

I’d also be tempted to assign reserved IP addresses for all Sonos devices in your router, if the router allows that. 

Still Get the issues

To save us guessing, please say which of the above you have tried. 

Both

Both actions suggested by @GuitarSuperstar?

The suggestions from both @GuitarSuperstar and @Airgetlam?

You really need to be a bit more forthcoming if you want help, @elangsru! 

If you assigned the static/reserved addresses did you power down all your Sonos, reboot the router then power the Sonos back up?

Some times that is needed to get the router to drop the old addresses and Sonos to pick up the new ones.

@nik9669a both as in rebooting the devices AND reserved IP addresses

@Stanley_4 I did not reboot the sonos devices AFTER reserving so I will try that as well. Though I have rebooted my router several times.

It's worth mentioning that my wife also experience these issues on her iPhone. Sometimes she does not  see a device on her phone whereas I do.

Also when I use the airplay mode on iPhone I can see all the devices, but If I select the hidden devices it will not connect. 

The devices reappear every now and then so it's not that they are gone all the time. Its been stable for a few days now, but I must say it has happened quite frequently last couple of weeks.

The IP thing is a long standing issue, a bit of a pain to do this fix but once done you only need to add any new Sonos until you change routers.

You might have another issue if the assign and reboot everything doesn’t fix you up but it is a good place to start and eliminates it as an issue if you still need to call support later.

Hi @elangsru 

Welcome to the Sonos Community!

I can see that all your speakers are currently connected to our cloud. I recommend you get in touch with our technical support team who have tools at their disposal that will allow them to give you advice specific to your Sonos system and what it reports.

I hope this helps.

OK thanks, I will if the problems continue. As of now it's been stable. Since I followed @Airgetlam advice of static ip addresses