so i'm no professional at medibang and certainly can't speak on behalf of the company with regards to certain issues but i do know a few things.
i'm not 100% sure what the issue may be but i'd check your correction settings (shown below) if your using the desktop version (I've not used mobile so i don't know how that layout looks of works)
like in the image i usually have it set to 10 to help with smoothing. I'd also suggest checking the settings for the tablet your using. it'll vary by brand so i can't quite direct you on where o go unless your using wacom but something related to either pressure sensitivity or tip feel for pen settings
like i use a wacom pen and touch small so under tablet preferences i'll change the settings here
sorry if this doesn't solve your issue but i hope it helps. you can also consider using medibangs help thread so feel free to give that a look too