help! ghost products

Hi, I have a big problem, nobody seems to figure out what to do!
I have an e-commerce developed with Woocommerce, with more than 2 thousand products. For a year it has happened that some apparently “normal” products (they are displayed correctly via direct url, or from the backend of “All products”) but do not appear within the categories they belong to, despite the product being published! (no draft, no private, no Uncategorized); in fact, it happened to me that these products were purchased by people who have accessed them through external research (google, social media, etc.) but within the category they belong to, they continue to be invisible.
During these months I made many attempts, I tried to deactivate all the plugins and the theme to see if it was a conflict, I changed the theme, I expanded the web space of my hosting thinking it was a memory problem, I contacted woocommerce (bad support ), asked in many forums, eliminated all products and recreated them all over again (work lasted 2 months) …
I specify that for the management of the Woo warehouse I use an external management software (Danea), but that the problem was already there before I started using it.
Hope someone can help me! I had to shut down the site by putting it in maintenance mode due to too many problems it was causing me.