Please be aware of this setting.
If you decide to use the packing method 'weight based', you need to enable the containers for weight based packing.
Disabling the containers for 'weight based' Packing.
If you were using the weight based packing method and decide to change your packing method.
STEP 1, You will need to, untick the setting that enables the containers for weight.
STEP 2, Then click 'Save Changes'
Now you can go ahead and change your packing method.