The catalog API is only returning 1 page of search results. For example, with AvatarEditorService:SearchCatalog(), if you perform a search request which has IncludesOffSale=true, the resulting Pages.IsFinished will always be true.
local CSP = CatalogSearchParams.new()
CSP.IncludeOffSale = true
local Pages = game:GetService('AvatarEditorService'):SearchCatalog(CSP)
print(Pages.IsFinished) --[[returns true]]
Pages:AdvanceToNextPageAsync() -- Errors
This issue also occurs on the website catalog. You can’t load more than 1 page of results when you “Show unavailable items”. Try loading the second page of results on this link here