I've unwittingly disconnected my sub and one SL speakers from surround

You need to remove the bonded surround speakers that you’ve mistakenly added before you can go back and re-bond the correct pair of speakers. 

Make sure that you haven’t turned off the WiFi on your sound bar since the surrounds and sub connect to the soundbar, and not either the surrounds or sub will ‘bond’ if the WiFi has been turned off. If you indeed have the ‘other room’s’ speakers bonded as surrounds, you don’t need to worry about the WiFi, they can’t be ‘bonded’ without the WiFi on.

Basically, you need to un-bond every device from your sound bar, and then carefully re-add them back to that ‘room’. It would be likely helpful if you’d set up your surrounds as a stereo pair in another ‘room’ first, but it isn’t required, just helpful.

To clarify: if the One SLs have been paired in another room they should be unpaired first, before adding as surrounds. 

I have lost my sub twice and my surrounds, ceiling speakers powered by Amp, once. I find it useful remove them, due a factory reset, and add them from scratch.

Network problems, most likely wireless. I’ve never lost any home theatre satellites. 

I don't know what caused this, but I do run everything wirelessly. I have very good WiFi - 400 Mbps and an a three satellite Orbi mesh system with two of the satellites hard wired.  All my streaming is rock solid everywhere in the house and I stream plenty of 4K content.  

Inbound data rates are only part of the story for Sonos, and in any case are mostly irrelevant above a dozen Mbps. The system totally depends on local connections between devices. The satellites connect via the master HT player. If the network infrastructure is being awkward it might refuse an IP renewal, since this has to be proxied by the HT master. Systems in WiFi (“wireless”) mode have occasionally struggled with this issue since the option to connect directly to the WiFi was first introduced.

I appreciate all the responses here, once I had pretty much given up I connected my old Orbi back to the main  router and then changed the network and once I did that I was able to add all devices back-BUT, only to the orbi network, even though there is an additional wifi available in my home it only connects to the orbi. Once I try to switch networks they all go out and and cannot connect. I’ll be reaching out to support on that one as I cannot figure out for the life of me why any of the devices will not switch networks, just goes in circles for all connection steps and nothing ever connects. I have an ATT wifi/router and Orbi ran off that-upgrading orbi, hence the network switched initially-had it on ATT wifi for 8 weeks, now it just likes Orbi, stumped on that one. Again thanks for all the feedback, without it I would not even have tried that.

Unless you put the Orbi into bridge (access point) mode there’s a router in the Orbi primary node. Your network would therefore be divided into two subnets.

Sonos controllers and players all need to be on the same subnet. 

Either switch the Orbi to bridge mode, or ensure that all Sonos controllers and players are always on the Orbi’s WiFi. 

Ratty, yes, ran into that originally with the setup, but changed that after initial setup some months back, though I do hear that Orbi is better to use than ATT as my main wifi source due to ATT Gateway issues. Something I am considering moving forward.