The status a crawler receives is not always the status a browser appears to get. Pages that render an error message while returning 200 are a common and hard-to-spot indexing problem.
This URL returns 200, so a crawler receives the page rather than an error.
This URL does not return a clean 200. Google will not index an error, and a 404 that used to be a real page is worth fixing rather than ignoring.
None of these tools can tell you whether Google has indexed a page. They read your page and your server, which is enough to prove a page is blocked and never enough to prove it is indexed. That answer only exists inside Search Console, which is what Seomely connects to.