I peeked over at your uploads! Your three uploads this weekend were on all the same day, so that could be part of why the three uploads didn't equal more subs? Instead of the uploads keeping you on Fresh three separate days, they were only worth one boost.
I'm still fairly new to Tapas though! I'm just sharing some of the advice/knowledge I've seen around the forums
I had those couple big subs boosts at the beginning (I think I was high on trending those two days), then my subs pretty much evened out. Especially when you compare it to The Demon in the Sea where I got a big sub boost, then they dropped off, then I uploaded chapter 2 and had a big sub boost again. My The Love of a Werewolf graph is kind of similar to your sub graph, a couple jumps, the lowering some but evening out to a sort of consistent gain.
From what I've seen, 40 subs in a month is really good for novels on this site! I hope you get to 50 quickly too 