They clamped down on spam accounts recently and deleted a few real accounts by accident. Has your follower account adjusted in light of those changes?

Do you want to compare boost reads? I've had a few and it might be normal. They don't always do fantastically. And the ups and downs might also just be normal Medium-ness because it's a bit like that.

Weird that it coincides with the new accounts though. It does sound like a big job to block them.