Some contect, the tractor randomly appeared on an intersection in the middle of the city. My two teammates weren't able to see it and for them I appeared to be hovering mid air. It's obviously the rusty tractor, but why is it green? Where did it come from? And why couldn't my mates see it? We were in an empty lobby by ourselves by the way.
https://gta.fandom.com/wiki/Tractor
I'm guessing it's a bug/texture glitch. Since your mates couldn't see it, I guess it was loaded by error or very likely by a hacker. Probably your game couldn't handle it and the texture loading for it went wrong because of that.