Overworld netherportal does not work, player teleports to overworld without generating new portal

On play.cwoare.nl I was trying to connect a netherportal with an end portal location in the overworld but for some reason this doesnt work.
I've tried placing the overworld portal in different places and the nether portal in different places and i'm 100% sure the nether coordinates allign with the overworld coordinates, i've even made a portal that had the exact alligned coordinates but the overworld portal can not be found and the player is placed at a specific location without generating a new netherportal at that location.

I made a recording and placed it on youtube:
Youtube Video Of The Issue

To get seed information you should contact the owner of this server at glennrietveld8@hotmail.nl