Wrong leaderboard ordering and `N/a` scores discussion

1. Wrong leaderboard ordering

Sometimes the ranking on the leaderboard does not follow the order from the primary column. It happens several times and we can hardly reproduce it. Once a competition starts to have a scrambled ordered, it stays this way, but the problem does not appear again when re-uploading the same bundle and submissions.

Issues:

• #1284
• N/a scores still ranked first: #2321
• #1171 <-- P1
• Another example below in comments

2. N/a scores

We have several issues that report N/a scores on the leaderboard. N/a is a replacement of score shown for a task not found. The problem is that the scores and tasks are separate and are sent to the frontend where they are matched and then scores are shown for a task or several tasks. This opens room for inconsistencies.

I propose to make the leaderboard on the backend and just send it to be displayed without any extraction or computation. This way we will never have n/a scores.

• a) N/a when submission rule is "Force Last"

• #1055

• #1275

• b) N/a for multi-task when submission rule is "Force Last"

• #2211

• #1174

• #1570

• c) N/a score after auto-migration (#2239)

• #1472

• #1174

3. When multiple tasks, how should we order the entries?

Right now it seems that the ordering is based on a sum of scores across tasks.

4. Request: separate leaderboards for tasks

• #1392

No files, tests, or entry points are named. Start by tracing the leaderboard ordering and score/task matching described across the backend and frontend, then review the linked issues for existing decisions. Done would require an agreed scope that resolves the ordering and N/a-score behavior without leaving the separate-task ordering questions open.