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 Sonos devices 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.  To cure this, do the following:

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.

It appears so far that simply restarting the eero mesh solved the problems. Will update if this changes. 

Restarting the router (when devices are off, sometimes while they’re on) often fixes issues with the DHCP table in the router. Which is pretty much what @jgatie’s entire last paragraph is about. 

But only one easy step.

Are you following the Eero-specific advice on

One easy step, for temporary results. Reserving IP addresses would keep you from having to do that ‘one easy step’ repeatedly, as a router that gets in that state once will most likely do it repeatedly, and at inconvenient times.