Works fine in v2024 but when updating to v2025 picture fields no longer display in the View modal.
They show on the Edit modal fine.
You may press F12 in your browser, go to Console and check for JavaScript errors, then go to Network panel to check for response error (e.g. server side error or wrong URL).
It was calling the right URL so that was pointing to .htaccess or router.php issue.
Router.php in the developer environment was causing direct /files/ URLs to be routed to index.php causing 404 route errors, meanwhile the API endpoint URLs worked because they were being handled by PHPMaker's routing.
So the solution was just to edit router.php. Solved.