[Champion Select] Wrong rune page in-game

How to reproduce :

1. Set your masteries during champion select. In this case, I used R-1111.
2. Save while having two free slots.

What's expected :

• I enter the game with my masteries.
• I enter the game with related masteries.

What happened :

• Masteries S-1231 D-201 were given to me that had nothing to do with my R-1111 choices.

Possible solutions :

• Dynamically allow more time if someone's mastery panel is open.
• Let people change masteries during the loading screen.
• Fill the unoccupied slots with random masteries. It's better to have 3-2 wrong masteries than all 9 of them.
• Save the selected mastery page index and summoner spell for each champion per role per map in a local JSON file and load it when the correct champion/role/map is selected.
  • This would also prevent having the wrong summoner spell because you played support last game and now you're jungle.

Single definitive possible solutions vastly outnumber the root cause of the problem. I don't know why it's still a thing.