404 Response on Links ending with Slash ( / )

404 Response on Links ending with Slash ( / )
Permalinks settings:
/%category%/%postname%/
Tried Fetch via webmaster, result:
Temporarily Unreachable
Checked indexed pages via Site:, result:
certain pages are already indexed

Is this something ’cause I found few similar concerns while looking for the solution.
Certain pages are already indexed including those listed from pages with errors (404 response). So which one should I believe, the indexed or the 404?
Should I replace this /%category%/%postname%/ with /%category%/%postname% (just removing the slash)
or change settings to -> https://www.domain.com/sample-post/