My son is doing a project for school and needed a car design printed. I downloaded about 8 different car prints from Thingiverse and I am having issues with all of them. Everytime I print them, about 30 minutes into the print, it starts getting messed up. It seems as if the bottom layer starts to move and from there the print is ruined. I have tried this on two different printers and I now have the new Sindoh 3DWOX 1 printer and the same thing is happening. Everything else I print seems to work great, it just seems like it's the cars that won't print. I don't understand what is going on or what I could be doing wrong. The bed is leveled and I have printed about 10 other things from this printer and they all come out perfect except for these car prints. Does anyone have any ideas?

Thank you.