I implemented ADS in recycler view every 3 items but repeats the first 3 items everytime

Question

I tried implementing ADS in recycler view every 3 items but instead of following the next items in the list of items, it repeats the first 3 times over and over until the list.size() is over. AdMob , ad item in Recycler View hides some items and creates spaces after the ad For achieving this, i tried to implement this code abovein my own code and it works fine except for the repetition of the first 3 items. The code is modified to satisfy my needs, so it may seem strange.

open class AdsAdapter2(override val activity: FragmentActivity, var dataSet: MutableList<adslist>, protected var itemLayoutRes: Int,
    showSectionName: Boolean = true) : AbsMultiSelectAdapter<AdsAdapter2.ViewHolder, adslist>(activity, R.menu.menu_media_selection),
    PopupTextProvider {
    var onItemClick: ((adslist) -> Unit)? = null
    private var showSectionName = true

    init {
        this.showSectionName = showSectionName
        this.setHasStableIds(true)
    }

    open fun swapDataSet(dataSet: List<adslist>) {
        this.dataSet = ArrayList(dataSet)
        notifyDataSetChanged()
    }


    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        if (viewType == AD_VIEWTYPE){

            val v = LayoutInflater.from(activity).inflate(R.layout.item_favourite_card, parent, false)

            return ViewHolder(v)
        }
        else{
             val v = LayoutInflater.from(activity).inflate(itemLayoutRes, parent, false)

             return ViewHolder(v)

        }
    }

 override fun onBindViewHolder(holder: ViewHolder, position: Int) {

       val card = getCardForPosition(position)
        if (card == null){
            Picasso.get().load(R.drawable.default_artist_art).into(holder.image)
        } else {


            // holder.courseNameTV.text = song.artistandname
            if (card.img == 0) {
                Picasso.get().load(card.img2).into(holder.img)
            } else {
                Picasso.get().load(card.img).into(holder.img)
            }
        }
    }

    override fun getItemCount() = dataSet.size + (dataSet.size / ITEMS_PER_AD)

    override fun getIdentifier(position: Int): adslist? {
        return getCardForPosition(position)
    }


open inner  class ViewHolder(itemView: View) : MediaEntryViewHolder(itemView) {

        protected open val adslist: adslist
            get() = dataSet[layoutPosition]

        //  val layoutposition: LinearLayout = itemView.findViewById(R.id.layoutposition)

        init {
            itemView.setOnClickListener {
                onItemClick?.invoke(getCardForPosition(position)!!) //WHEN AD CLICKED ==NULL
            }
        }

        val img: AppCompatImageView = itemView.findViewById(R.id.image)
        val layput: MaterialCardView = itemView.findViewById(R.id.imageContainer)
        //  val layoutposition: LinearLayout = itemView.findViewById(R.id.layoutposition)
        val layout: MaterialCardView = itemView.findViewById(R.id.imageContainer)
        val image: AppCompatImageView = itemView.findViewById(R.id.image)
        val title: MaterialTextView = itemView.findViewById(R.id.title)


    }



    companion object {
        val TAG: String = AdsAdapter2::class.java.simpleName
        const val ITEMS_PER_AD = 3
        const val AD_FREQUENCY = ITEMS_PER_AD + 1
        const val AD_VIEWTYPE = 0
        const val CARD_VIEWTYPE = 1
    }

    override fun onMultipleItemAction(menuItem: MenuItem, selection: List<adslist>) {
        TODO("Not yet implemented")
    }

    override fun getPopupText(position: Int): String {
        TODO("Not yet implemented")
    }

    override fun getName(model: adslist): String? {
        TODO("Not yet implemented")
    }

    private fun isCard(position: Int) = (position + 1) % AD_FREQUENCY != 0

    private fun getCardForPosition(position: Int): adslist? {
        val offset = position / AD_FREQUENCY
        return if (isCard(position)) dataSet[position - offset] else null
    }

    override fun getItemViewType(position: Int) =
        if (isCard(position)) CARD_VIEWTYPE else AD_VIEWTYPE


}

The logic of knowing which part of the list is gonna be an AD or a CARD is explained in the answer of the url above and it is applied on the last 3 functions and i do think the problem resides there but i cant see it clearly.

I'm not a super developer so it could be something so simple