I have automated and streamlined the process (I have also fixed the main issue which results in the level check boxes section not appearing, though there are still a few out there)
Once you access the MP, it will automatically check if everything is running smoothly and that the level links are showing. If they are not you will be redirected to a help page with 3 options. The 1st option is usually all it takes to fix the problem. Click the link and you should be redirected to your MP with everything showing and working just fine.
If it does not, you will be returned to the help page. Here you want to try the second option, clicking the link again and heading to the MP to find everything as it should be.
In the ultra rare event that you have to visit the help page a 3rd time, you will be instructed to contact me via PM or email for assistance.
Everything should work for you now automatically without having to perform a level reset or delete your progress. Please note, though, that level progress is not stored until the MP is working correctly. If you experience this issue after beating a few levels, you will need to revisit and complete those levels again for the links and check marks to show up indicating you have solved those levels. There is nothing I can do about this, I'm afraid.