is this bug in kotlin recyclerview?

For some reason, nofityItemRemoved only affects the item that is removed and allows all subsequent item numbers to go out of sync. So you need to follow it with a call to notifyItemRangeChanged.

fun removeItem(viewHolder: RecyclerView.ViewHolder){
    removedPosition = viewHolder.adapterPosition
    removedItem = arrayList[removedPosition]

    arrayList.removeAt(removedPosition)
    notifyItemRemoved(removedPosition)
    notifyItemRangeChanged(removedPosition, arrayList.size)
}

This answer on a similar question states that if you do it this way, you get a proper animation of the item being removed, but I haven’t tried it:

fun removeItem(viewHolder: RecyclerView.ViewHolder){
    removedPosition = viewHolder.adapterPosition
    removedItem = arrayList[removedPosition]

    arrayList.removeAt(removedPosition)
    notifyItemChanged(removedPosition)
    notifyItemRangeRemoved(removedPosition, 1)
}