Hi thanks for reporting the problem.
[1] Users need to review at least 5 minutes a day for their data to be reflected in the leaderboard leagues, so short time will be counted as an absence.
If so and if you want to fix it, these calculations are based on data in decks so you can fix them by changing the date on the PC and reviewing the cards. (Same way to fix Streaks)
- Turn off Wifi on your laptop.
- Manually change the date to the day you lost the streak.
- Open Anki and press “x” to close the popup that tells you the time is wrong (if you press OK, Anki will close.)
- Review a few cards. (Unimportant cards)
- Repeat until the total time is 5 minutes.
[2] The next day start time in Anki is different from the next day start time in the leaderboard. Please make sure that the next day time on the leaderboard is correct in Setting.
[3] If these are all unrelated, perhaps there is something another problem. If so, you will need to send me your deck so that I can look into the cause.
As Danika_Dakika says Add-on is not related to official Anki’s Anki so basically there is no official or community support. Here is the support thread for the leaderboard at AnkiForums.