Google Home, as it turns out, is just as susceptible to dust as other electronics out there, and can even stop hearing your commands if enough dust collects. Dust can play merry havoc on all sorts of electronics in all sorts of ways, and blowing that dust out, with something like a can of compressed air, is usually the answer. As it turns out, that's another thing that Google Home has in common with other gadgets like game consoles and computers. The symptoms include a Google Home unit spinning its lights, but giving no indication that it intends to answer your inquiry, or that you've stumped it, leaving no way to tell if it heard you clearly. There is a way to check for this issue, but a quick blow into the two mic holes of a misbehaving Google Home may be faster.
Stories of errant Google Home units being sorted out by blowing into the mic slots litter enough of the internet that any unresponsiveness may warrant blowing into the mic slot. If you would like to check, you can always check out your Google recordings for any that sound garbled, distant, or muffled; these are a dead giveaway that your unit has some sort of physical difficulty hearing you, most likely dust. In order to check, go to Google's "My Activity" page. Everything you do on Chrome, Android, and other Google services is stored here for you to observe, back up, or delete as you please, including audio recordings.
If blowing into the mic and a factory reset, performed by holding down the mic button for about 15 seconds, don't do anything, you may be looking at damaged hardware. While software issues could theoretically occur, as with almost anything else with a CPU in it, though most of the major issues on the software side seem to have been sorted out at this point. Google Home units reportedly have a Chromecast at their core, with some special software tweaks to run Assistant and connect to the cloud, so there is the possibility of issues on both the hardware and software ends.