It's the complete opposite for me! While Tapas has stagnated, my Webtoons has been growing despite having a months-long hiatus!
My experience with Webtoons has been a pretty positive one overall, but I believe my experience is very different from most regular users. For one, Webtoons regularly featured my work (I think I'd been featured in some way several times on Webtoons, whereas Tapas I've only gotten a feature once).
Once I did have that growth though, one thing I did was reply and engage constantly! I asked a ton of questions in comments and asked readers what they thought of the day's update or who their favorite characters were. It built rapport and now I have a steady return of regular readers!
I also find that when you engage and comment constantly, shy readers are also more likely to comment!
Another thing I did was include bonus content every other update when I could. This helped explain my thoughts for an update, or talk about a featured character. It helps immerse the audience!
And one final thought: Promoting on social media should also include dropping links (within reason) to things like art share threads or joining communities on Discord to help improve your work! I found since joining these groups (outside of the platforms themselves), being able to get constructive, helpful crit helped my work take better shape!
Hopefully that helps? ^^