The closest things I can see are that the logins are showing up as almost exactly 30 days apart; the system sends an inactivity warning a few days before that 30 expires however, so if you're consistently doing it 1 month apart it'll almost always send that email.
The most recent suspension may have been caused by a slight gap I can see in the logs however; there was a login on 1/1/18, and another on 2/1/18 which is when the inactivity suspension was removed. There are 31 days in January however, which would have meant on 1/31 a suspension was queued (and eventually executed very early on 2/1, approx 10 hours before it was unsuspended by you).
The best advice I can give here is to shrink the login window slightly; when we used to require logins every 14 days (which was a few years ago granted), I did my logins on Mondays just to ensure if I missed one, I would be close to the time but not past. If you're wanting to avoid the inactivity warning email, I would recommend doing logins about once every 21 days instead, which should be enough to avoid the email (and give you some buffer room in case something happens and you miss a day or two).