I have a Google Mini and Google Nest Hub. Since a few days ago both devices couldn't answer basic questions or follow basic commands. For example, I would ask about the time and weather. The Mini would say "I don't understand" while the Den Display would respond with "I don't know, but I found these things on search." Another thing is that whenever I play music recently, I would ask it to stop after an hour, which it would say "Den display will stop playing in one hour," but actually wouldn't.
I'm sorry to hear that your Google Home Mini and your Nest Hub aren't working as it should be ― let's go ahead and check it out. Is this the first time this has happened? How far are your Nest speakers from your router? It would help a lot if you could do a sequential reboot by unplugging the power cord of your router followed by your Nest speakers. Plug them back in after 3 minutes starting with your router. Restarting your phone might also help.
Keep us posted.