Hi @MCT567
Welcome to the Sonos Community!
If the only problem you have with your system is when trying to group, then it’s likely that your WiFi mesh nodes are using different WiFi channels from each other.
When Sonos speakers group, they exchange data directly between themselves, bypassing the router, by communicating on the same channel as the WiFi. If your different WiFi nodes use different channels, the speakers will be unable to find each other using this direct method. I recommend you check your WiFi settings and put all nodes on the same channel.
If you cannot do this, wiring one speaker permanently to the main WiFi node with an ethernet cable will probably be the best step you can take to improve the function of your Sonos system. Please keep it 1m away from the node, to reduce interference.
I hope this helps.