Ok, I have fixed it all for the first form (Fitnessprogramm). A default search for ALL on each select still only had 3 results. It should have 7. This is because four products have no price. I have renamed the products and their slugs to make debugging easy. I changed the price slider to auto detect the range. You had this at 0-1000, but the true range (of 3 that have a price) is 250-2000. This would have caused product 32 to be missing from the search, as it is priced at 2000. With the fixed price slider ….
Products 31, 32 and 34 have a price and show on the ALL (default) search:
http://50.87.163.18/~websysdy/projects/fitparison/search-result/?_sfm_preis4=250+2000
See how a default search still has the price slider range?
Products 19, 22, 24 and 26 have no price and so are missing from the results. If you edit the search url to exclude the price slider range:
http://50.87.163.18/~websysdy/projects/fitparison/search-result/
All 7 now show.
So you can see the effect of manually setting a price slider range versus auto, and also the effect of having a price slider when not all products have a price.