When trying to fit ships via the multifit spmetimes something is forgotten, like some ammo for example and you can see whatever it is by clicking on the … next to missing ships and/or equipment.
Can an option be added to ignore the missing items and fit with what you have anyway, often I have forgotten to get ammo or other charges and I have to manually add everything at that stage,
You have to remove that thing from the fitting itself before you start Multi-Fitting. Multi-Fitting does not allow you to change the fitting during the fitting process like you can add/remove items from Multi-Buy.