Tools said everything was fine, but Search Console lists pages with a missing field

Older versions checked each schema against one sample page, and preferred one with a featured image, so posts without an image were never looked at. Every post, page and product a schema covers is now checked. Open Schema Pro → Tools → Validation: Page Checks lists, for each schema, how many pages are missing a required property, which property, and the first 50 of those pages with links to edit them.

If it says "Not checked yet", press Check every page now. A large site is checked in the background over several runs, and the panel shows how far it has got. After you fix a post and update it, that post is checked again as soon as the save has finished. Archives, search results and the blog index are not part of the check.

Each line there, on the Dashboard and in the post editor's Schema Pro box, starts with Error: or Warning:. An error is something the schema itself lacks, so fix it in the schema. In Page Checks and the post editor, a warning is something a post fills in for itself, such as its featured image, so fix it on those posts. On the Dashboard a warning can also be advice about the schema itself, such as a rating given without a count or a salary without a currency; the line says which, and that kind is fixed in the schema.