I have eight speakers which were all connected to my Google home at one point (Google home minis, or Google mesh hubs with speakers). They were in different speaker groups, but now I can only see two of the speakers in the groups. If I tap on one of the speakers from the home app that is not available for a group it says "connecting" then shows the volume, but that speaker still fails to show up in a speaker groups. I've tried making new groups, but only the two speakers are available for a new group. I removed one Google home mini from my home app with the intention of adding it again, but now I can't even add it back.
Thanks for posting here in the Community forum. We'd love to help.
Check if the Google Home speakers missing from the speaker groups are still working individually. Ensure that the Google Home app is up-to-date before you try to create a new speaker group. If they're still not showing, reboot all of your Google Home speakers for a minute.
Let me know how it goes.