I also experience sub loss every time I update. I have over 1,300 subs right now and I only got there because I was lucky enough to be featured on the banner in discover and somewhere else on the app. But I don't gain subs if I don't get help from exposure. However, my readers are pretty engaged so I honestly don't mind too much. As long as the views go up and people are commenting and enjoying it, that's all I care about.
But I have some speculations as to why this has been going on. I've been seeing a lot of people noticing sub loss for at least 9 ish months now and there's only a few factors I can think of:
1.) Webtoon changed their algorithm. I feel like every since the ad revenue program went into play that is when the sub loss started happening. You need to reach a minimum of 1K subs and 40K views to apply, and there's a theory that perhaps Webtoon is manipulating it for comics that are about to reach that mark. But still, it's a silly theory and probably has no weight.
2.) There are a lot of bot accounts and Webtoon is in the process of eliminating them. I have seen first hand a bot account comment on one of my episodes.
3.) Since the max number of comics you can sub to at a time is capped at 100, perhaps people are subbing to others and thus unsubbing by accident?
4.) Just more comics on Webtoon.
These are just my thoughts so really, until Webtoon addresses this issue, no one will really know what's going on.