Placing mesh will randomly offset to another location and cannot be moved with gizmo

Hi guys, I am new to UE4, while playign with UE i met some problems and after doing some google search, still not find any helpful info, so i posted here. BTW, what are some other great UE4 forum that i can find some great resource? i would love to go check it out(except the offical forum)
My problem is whenever i place my mesh in the level, it wont be place on the ground. it would always offset a lot, sometimes in the sky, sometimes into the ground. the Location sometimes were at (10000,-10000,-10000), all the mesh were form package i download from marketplace or Megascan asset. which should work fine. I have no idea where did i messed up, how can i fix it?
BTW, i cannot move the mesh with gizmo(though i can rotate or scale it with gizzmo), but i can adjust the location in details panel
Thanks, hope you guys doing good!

Make sure the grid snaps is turned off, or you can lower the snap distance.