AttachTo: “/Game/STF/Pack03-LandscapePro/Maps/UEDPIE_0_open_world_LSP_v2.open_world_LSP_v2:PersistentLevel.Landscape_0.RootComponent0” is not static. Cannot append “/Game/STF/Pack03-LandscapePro/Maps/UEDPIE_0_open_world_LSP_v2.open_world_LSP_v2:Persistent

Right click on the actor that is causing the problem and detach it.

Or you need to make the mobility of both actors the same in the details panel.