I get that it makes you feel bad.
Here's some reasons why this might have happened tho that are unrelated to you as a creator:
They deleted their account.
They stopped using tapas all together. I know I haven't opened tapas for about a year really before I came back and I was close to deleting the app altogether a few times
They are in a different headspace now then when they started reading your comic.
They just weren't an active reader from the start.. Having someone who won't engage with the subed series is worse than not having them subbed at all
But also, you are 8 episodes in. Things still fluctuate a lot. People sub for now without knowing where the story is going, and every new episode shapes the tone and stuff.
The further you are into the story the easier it is for readers to tell if they will like it.
But right now it is completely normal for readers to figure out that this might not be theirs after all.
It's just taste!