by observation established the following
bindings to categories are reset at night, then restored during the day
here is a screenshot taken around 8 am
https://prnt.sc/10grnc8 . number of products category 29
here is a screenshot taken at 9 am . the number of category products is already 31
the checkbox "do not disable the product if it is out of stock" is enabled, so we exclude the hiding of the product by availability.
please see what is the reason