Some items not shown in category lists when choosing "sort by price low/high" (1.7.6.1)

[Selin0r]

Hello community,

all items which were added in the beginning, are shown perfectly in categories – no matter if sorted by name or price.

However, all items which are beeing added now, disappear from category lists as soon they are sorted by price (low to high and high to low).
 

• Example for working items (sort by price > items are shown)
  http://shop.reflecta.de/index.php?id_category=10&controller=category&id_lang=2
  http://shop.reflecta.de/index.php?id_category=10&controller=category&id_lang=2&order=product.price.asc
  
  
   
• Example for disappearing items (sort by price > items disappear)
  http://shop.reflecta.de/index.php?id_category=12&controller=category&id_lang=2
  
  

Does anyone know how to fix that? Maybe some error in the DB?

Thank you very much!

Edited June 19, 2020 by Selin0r (see edit history)