1 - Surprisingly, when I start a new game, the game runs normally without any error messages! However, the font's outline thickness was not applied.
2 - The core plugins I am using are the most recent versions.
Viewing post in Hakuen Studio Font Manager for RPG Maker MV-MZ comments
Ok so we figured out the error and that is it. You will need to start a new game.
About the font outline, if you are not using any other plugin, then try put the alpha value to 1 instead of 0.5 to see if you will be able to see better the outline.
Otherwise, send me a sample project replicating the error on my discord: hakuenstudio