Best answer by Airgetlam
First thing, don't "re-add" the speakers, or "factory reset" them. Never a good idea, unless specifically suggested by someone from Sonos. Fortunately, you've got other speakers that are holding on to your data for you, since it's not stored in the controller app.
What I'm thinking you're running in to is an issue with duplicate IPs, often exposed when you update Sonos software, due to the soft reboot function.
My suspicion is that while rebooting the router is a good thing, you may not have unplugged all of your Sonos devices before doing it. So, when the router came back up, they tried reconnecting to the same IP address that they were connected to before rebooting.
There's 2 ways of dealing with this. The first is to unplug from power all your Sonos devices. Then reboot your router. Go to the first Sonos device, and plug it back in to the power. If you have one (or more) of your Sonos devices connected to the router, do that one (and only one) first. If you don't have one connected to your router with ethernet, no worries, just plug in the one that's physically closest to the router. Give the device (I don't say speaker, because you might have a BOOST or BRIDGE) a minute to boot up, and then move on to the next one. Complete that process for all of them, allowing each one to fully boot up before moving to the next.
But that's a short term fix, potentially. i.e it could happen again. If you prefer, go in to your router's set up and assign reserved IP addresses for all of your Sonos devices (and while you're at it, do pretty much everything else). This usually requires a review of the router's manual, each company seems to do this process slightly differently. That should be a much more permanent fix, and this duplicate IP address issue shouldn't occur again.
Hope this helps.