Yeah, boosts seem particularly vulnerable to the weaknesses of the algorithm in the first few hours. Unsurprising, I guess. Put a blindfolded chimp in a shopping cart, and they might veer a couple of yards off course; strap 'em into a drag racer, meanwhile...
And once that wrong course is taken, and the algo gets the signal that 'no one's reading this' (because it's being sent to meaningless, inauthentic users), the damage has been done.
Effectively, Medium does its thing and reaches the conclusion 'this article is rubbish', whereas the correct conclusion is 'our algorithm and bot-filtering are rubbish'.
And it's hard to argue with that kind of cognitive dissonance (75 million pieces of evidence for that from last week...).
It's frustrating, and as you say, getting more erratic. Yesterday - out of nowhere - I had 570 views. The number should have been 200 or so, based on regular read ratios. I have no idea what those 370 views were of - it wasn't even my recently boosted story, or anything published in the last couple of weeks.
So some group of users has somehow dug out older pieces by me, clicked on them en masse, and then departed. Why? How? To what extent can one rely on a platform that acts this way?