variable in c++ resets to nullptr in unreal engine BP

Hi, I would appreciate your help.
My project is on version 5.0.3.
I encounter a really annoying problem that I initialize a class variable in c++ and it resets to nullptr in unreal engine BP and this prevents my ai from following the player.
I’ve already checked everything many times and I can’t figure out where the problem is and when exactly it happens.
in Blueprint I only use the variable as Get.
I don’t know what to do anymore, Thanks in advance.

Ok, so I found out that when the AgroSphere is on different surfaces it resets. Can anyone help with this?
I think it’s something with the settings of the collision.