Have you “reserved” IP addresses in your router?

No. What do I need to do for this? 

Connection problems which appear suddenly are often caused by network problems, not Sonos problems. The typical cause is duplicate IP addresses. These often show up after an update or power outage because a reboot requires the device to request a new IP, and the router, having lost track of current IP assignments, issues a new IP that is in use by another device. Rebooting the router may offer a temporary respite, but in reality it exacerbates the situation because the reboot simply loses track of the IP assignments all over again. You need to do a complete refresh:

Reboot/power cycle your devices in the following order:

Modem
Router
Switches or hubs
Wired Sonos units
Wireless Sonos units
Computers/printers
Wireless devices - phones/tablets etc.

Allow each device to come back up before proceeding to the next. Note that you can permanently prevent duplicate IP addresses by assigning an IP to each device's MAC address in the router setup. See your router manual for details.

Usually the router’s DHCP Settings page will let you do this easily and often has a “help” screen to give you instructions.

Same here. i bought this Era 100 to have nice sound when traveling in US, and staying in different apartments that don't have audio systems.

The first apt worked first time OK, however later had to reboot router once. I thought could be one off issue,  poor router etc. Doesnt seem so, as second home same issue and here router can't be reset as nowhere to be found. Probably different floor .

Major PITA when ALL devices (iPad. Phones. Laptop, Roku connect just fine and have connection marked as EXCELLENT but Sonos does NOT connect. It finds the speaker but can't  simply change network, tried both with iPad and Android app.

​​​​​​Will try with support, however I guess their answer will be same "please reboot router"

​​​​​​Why other devices connect just fine and don't require such hassle.

Sure, I can connect bluetooth but that's not why I bought this speaker...

Community WiFi isn’t usually compatible with Sonos.

It is simple to configure a Travel Router that will work with Sonos as you move from WiFi system to system and it is far less aggravation than trying to sort out incompatible community WiFi systems.

Thanks for this info, very helpful indeed.

I got myself a ultra compact travel router (Amazon bestseller) and tool just 10 min to install, literally put a switch in share hotspot mode and configure via website connection to existing wifi that Sonos could not connect to, and voila after resetting Era 100 and fresh install and am now listening again to Sonos.

Sonos techsupport, while patient does not suggest more than the app does i.e. reset the router which I didnt have access to, and never suggested travel router option.

Also, bluetooth did not work since it requires the Sonos to have wifi connection, even if you just want to use bluetooth!