Hello, so you've set the stack multiplier values to "500 000 000" 500-mil which is the problem.
If you look at the items its complaining about ( Twitch Rivals Desk default stack size of 5 ) & then multiply that value by your ridiculous value set ( 500 million ) you end up with 2 Billion 500 million. "2,500,000,000"
The largest possible value in C# is 2,147,483,647 Which means anything over this stack size will break the plugin
( 2.5 billion is significantly more then the max stack size supported in the game.. )
So maybe you can do me a solid here and lower your multiplier values to a support level.