i think i figured it out, it was my pi-hole who was slowing things down.
i reinstalled the pi-hole, and no speed issues anymore on kodi devices anymore.
it is a bit strange to me, all my clients recieved 2 DNS servers from DHCP, first is the pi-hole, second is the backup Quad9 DNS.
only the Kodi client slows down, windows clients didn't have issues.