Ohio voters who saw the post going around a few hours ago: Today is not your last chance to re-register if you have been pruned for inactivity, you can re-register at any point before the standard voter registration deadline, which is one month before the election (Oct 7th).
Making sure you're registered to vote is still a good idea though, as many people's registrations have been removed! (If you are in Ohio and haven't voted in 4 or more years, your registration has been made invalid, and you will need to re-register.)
Sorry for spreading panic a bit, and thanks @h-land for looking into it further than I did!