Hey I already posted the issue (#109) and I though this will be fixed with the new update.
I update to version 2.0.5 but the same error is still appearing.

This will hopefully be resolved once we switch to another backpack mod in 2.1. That update is still ways away though, because the dev team is rather busy and burnt out by irl responsibilities.

If you read #109 again, the fix was unbinding things from your mouse buttons. Some mice have a problem with the backpack mod it seems where binding any control to their secondary buttons will confuse the game engine. So with these mice you just cant't bind anything to a secondary mouse button.