I did a speedrun on the Commodore 64, but when I submit a run I can only pick Amiga. Why is that?

Here is the speedrun (10:55)

It seems the version you are using is missing a level. Level 31 should normally be an outside level. The C64 version has 33 levels unlike the Amiga version, because the final boss is an additional stage. The high score screen even shows a score for stage 33. Maybe the hack you are using that offers additional levels messed up the levels.