That warning means you're using a TBox with impossible boundaries, in this case ones that go outside the client.
Code:
The client has a height of 600, thus the ye is out of bounds. Setting the value to 599 (h-1) for now.
This part means Simba has corrected the values for you, so if the performance of your script isn't affected, you can probably ignore these warnings.
The code you've provided doesn't look like it uses any impossible TBoxes, so I don't think that's the issue. If you want, you can debug the backpack's TBoxArray (tabBackpack.getSlotBoxes()) to make sure they're not doing anything crazy.