Weird "Objects Floating on the Ground" Bug/Glitch

m having a very weird glitch, just before taking down the helicopter(osprey) carrier (the one which land more units) everything starts to float, thats right, every thing moves like floating on the ground, and it is starting to annoys me
it happens until the part where you have to use a machine gun to kill a horde of vortigaunts, then it happens again when you have to blow up a tower and a gargantuan, (it happens just to the explosive boxes) and thats it, here its the link to the video i just uploaded, i move just a scrap piece of the osprey but you can clearly see what im talking about

https://www.youtube.com/watch?v=TU5GEHEry4Y

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