I installed and played the game many times and in my lastest playthrough I have a problem that I didn't had before.
It's in Riverwood. There is a seam between the outside world and the Riverwood's grid as you can see in the picture : https://ibb.co/DC3XGNS.
As I said, I didn't added new things in Riverwood place. I use only JK's All in One. And if I remove the JK's mod, The terrain is good again. It's as if xLodGen can't adjust the terrain of JK's SKyrim. And what's strange is that it was OK before. I reran xLOd Gen many times and there is always this problem.
Can it be a problem with a maximum number of mods ? I have 898 mods atm and 393 .esp .esl.