The page says “Not found”, but the server reports 200 OK. Google may classify this inconsistency as a soft 404. Other causes, including empty or unusable content, can produce the same classification.
Request a deliberately missing path
Choose a clearly nonexistent address on your own site without changing an existing product. Compare its status and content:
/product-that-does-not-exist/
HTTP: 200
View: Product was not found
Finding: The error view contradicts the success status
A custom 404 layout may contain navigation and useful links. It does not need a success status to provide those features. For a web application, inspect the initial server response as well: a later browser-rendered message cannot retroactively change it.
Find the responsible layer
Inspect routing, server rendering and the reverse proxy. If every unknown address receives an application shell with 200, the visible message may not be the source of the problem. Return an appropriate error status for a genuinely missing resource instead of merely changing its heading.
Then test both an unknown path and a working one. Existing content must remain reachable. Do not redirect every missing page to the homepage just to conceal errors. If a genuine content successor exists, assess a targeted redirect separately. Record the technical correction independently of any later Search Console result.