Finally found out why... It was because at the time of making the mech and uploading it to the workshop, I was using MPatcher, which must have changed something to cause the mech's data to be incompatible with the Vanilla game

Well thats odd, i've never had that happen before, granted this game has not been updated in a long time as far as memory serves so hell if I know

I have this problem with many other creations. I don't know if it's just me, or if it's a common problem.

whenever I try to select it in the load tab, it doesn't actually select it. The red highlights the name, but the mech itself doesn't appear.

looks great :D