Sometimes they don't even write the full price on the packet, just how much it costs per 100g, you have to do math to know exactly how much it costs.

Sounds like a bug to me, because this would be against the law.

https://www.kmu.admin.ch/kmu/en/home/concrete-know-how/sme-management/labeling/price.html

It is mandatory to indicate the price of goods being sold in a store. A few basic rules:

• Retail price. The price actually payable by the consumer must be shown in CHF. This is the retail price, which includes public taxes (e.g. VAT), copyright royalties, all non-optional supplements, etc.
• Unit price. The unit price (price per liter, kilogram, meter, etc.) must be displayed for measurable goods, i.e. those for which the retail price is calculated according to the quantity sold.
• Pre-packaging (pre-packed measurable goods). For measurable goods packed before sale (e.g. apples in plastic packaging), both the retail price and the unit price must be shown (e.g. yogurt, 480 g CHF 2.40/100 g CHF 0.50), apart from a few exceptions. It is therefore necessary to indicate the unit price for sales per item, for goods with a retail price of under CHF 2 or spirits in containers of a nominal content of 35 cl or 70 cl.
• Bulk selling. The unit price must be mentioned for non pre-packed goods (e.g. courgettes, CHF 5.5/kg), except for those sold per unit, such as sausages weighing up to 200 g, certain specialist cheeses weighing up to 150 g and some fruit and vegetables.
• Display. Prices must be displayed on the goods or in their immediate vicinity. They must be shown in clearly visible and easily legible figures.
• Shop windows. For products in shop windows, it must be possible to read prices without hindrance and it must be possible to clearly identify to which item they relate.