There is no logical explanation. APU sometimes for no apparent reason moves a dollar or two either way. It always (IMO) gets back on track in week or two.
It's known as 'an old lady stock' and sometimes the old ladies get nervous or need more money for Botox Shots..
I have owned this off and on for over 15 yrs. You can buy and hold,5 yrs. ago you could have bought this for 21.If you had held it well..... or you can buy ,let it go up to 2 days before ex-divd. ,sell, let it come back and re-buy. I've done both and have always made money.