Fogging can be a problem to diagnose. A minilab repair tech told me about a
lab that had an unusual fog issue, that only occurred on the first print
after the lab had been shut down for a period-- overnight, lunch break etc.
The first print would have an indistinct grid pattern image on it. Turns out
that the "box" that held the photo paper had a very tiny hole in the top,
sufficiently tiny to act as a pinhole camera and expose an image of the
ceiling (drop ceiling with grids and tiles). Since it was in a darkroom,
this image only showed up when the darkroom had been inactive and room
lights were on for a time.

As for your problem, the light coming under the door may be reflecting
somewhere to get to your print. You may want to check out the local home
center (Home Depot, Lowes, local hardware store) for some type of door sweep
or threshold that you can easily install. It's important to seal up the room
so that the dark can't escape!

Nicholas,

Thanks for your reply.  This may have further exacerbated the artifact,
as I did pull the prints early, as they were somewhat overexposed.  I
typically used 1 min for RC papers and 3 min for FB paper at 68 deg F.
I may try some further experimentation to recreate the problem, and
better define all the possible variables involved.

BTW, I am originally from Painesville, and spent much of my graduate
study time in Cleveland.  Hope all is cold and grey ;-).

Best regards,

Dave