Hunk of Junk challenge (Leia Hoth Skin part 2) stuck at 4/5

Yes, I confirm that this is the solution!

Try like this:

1. Play 2 (or 3) games until the finish

2. Quit to main menu

3. Repeat steps 1. and 2. five times

You will (I hope) then get the progress 5/5 and complete the challenge "Fastest hunk of junk".