@Pawel_Chojecki I’m going to respond to what I had just sent in a Support ticket to @Muhammed_K.
"Some good news, we have determined where this issue is originating from and understand it better. Even though it may seem like your item is missing, the issue is ultimately because the back-end (servers) and front-end (UI) are not accurately responding to each other and in turn not showing up in your listings. But, they are still on the back-end.
The bad news, we still need some more time to fix this bug, but now better understand what the issue is and can address it."
With this being said, we know what to ask for and what to be looking for. So can both of you do your best to list out any and all known items currently not showing up in your On Sale tab and either create a new Support ticket or respond to one that you have open.
Again we apologize about this and appreciate your patience. But rest assure, we will make sure that all listings that you have created reappear.