Splited Terrain Shadow Issue

Hi,

It's been two weeks I am trying to find what's the problem with the shadows from a realtime directional light on my PDG terrain. When I cook my nodes, all is well done and the shadows looks as it should be on the terrain but after working in the editor or going in play mode the shadows go wrong as on the picture.
I am on URP and I tried to play with all shadows and lighting settings but nothing happened. Need Help !
Thank you !

 

Update: It seems that it happen when I split the terrain in several parts. The shadows works well on whole terrain but are broken on the sliced version of the terrain.