@Alecomp : maybe you're righut :what is the size of this table cscart_product_features_values ? i've had a similar problem. the reason was in multiple time doubled products features. so when any filter was applied it walked through all these features.
Table cscart_product_features_values contains 1216 rows. We are using about 40 features, in 3 languages -> should we find about 120 rows in the table ? 1140 rows have an empty "Value" column.
Any idea to test and/or make corrections in that table ? Thanks a lot !