Why doesn't the price filter support specific prices?
Price filters do not take into account all specific pricing rules. For a classic customer group, only the specific prices applied to the default product combinations will be taken into account. Indeed, the price relevance calculation methods made available to developers by PrestaShop are imperfect. It is impossible for us to retrieve information on all the specific prices to integrate them into our filter rules.
Also, please note that the indexed price is the one in effect at the time of indexing. Therefore, if you often have to change your prices, consider increasing the indexing frequency so that your price filters are always up to date.