Thanks for reaching out. Sorry to hear about this experience. Could you please tell us when did you notice this change in its behavior? Aside from your Nest Mini, what other Nest devices are affected?
Let's go ahead and try first to perform a reboot simply by unplugging the Google Nest Mini from the power source for at least a few minutes. As soon as it's plugged in, navigate the Home app and adjust the equalizer to see if this would make any changes on its behavior. Lastly, it would be best if you can also try it using a different phone to see if there's any difference.
Keep us posted.
Thank you for your help. I have 3 devices and I first noticed this after adding the last one, a display. I have since followed your advice to do a full reboot on them and it appears to have resolved the problem. Obviously, I had tried a reboot before I contacted you, but this time I left them off for longer.