It's probably, because you were "better as intended".
When I did this fight yesterday (Luke lvl 33, IG lvl 34, Choda lvl 33), I was never able to reach 100% on Tier 3. I easily got to 90%, but then my damage rapidly decreased and eventually dropped to 1, so I could never get past 97%.
If you somehow managed to do that, the system seems to automatically flag it as cheating. Apparently, you're not supposed to complete Tier 3 with level 30 characters.
But if they have such a strict progression, the system has to work perfectly—and I highly doubt it does.