We're sorry for the trouble this may have caused you — let's see what's going on.
Were there recent changes on your network or set up? Try clearing the cache and data of your Google Home app then reinstall it. Also, creating a new home structure and setting up your Google Nest Hub Max there might help too.
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I had this issue last night after Factory resetting my Hub Max. I had removed it in the home app but still couldn't get it to join. The solution I found online was to go to my Google account settings - Data & Privacy - Third Party Apps with Account Access. Then find and remove Nest Hub Max. I also deleted and reinstalled the Home app from my phone. Now factory reset your Hub again and attempt to set it back up. This worked for me. Good luck!