Wargear Question

Making my first list, brand new and just starting to learn the rules. I'm trying to equip a Scout Squad with sniper rifles. The default squad is 4 scouts and a Scout Sergeant. The rule says, "for every 5 models in this unit, 1 Scout's boltgun can be replaced with 1 Scout Sniper Rifle". But it's giving me an error with the 4 scouts and 1 Scout Sergeant (5 models), but the error goes away if I add 1 additional Scout to the unit. Does that mean the Scout Sergeant doesn't count as a scout model for that unit or is it a bug in the app?

Also, do I understand that right that they can't all be equipped with the sniper rifles? Only 1 out of 5?

Thanks 👍🏻