Well, there’s your problem; I don’t know what about your configuration is triggering it, but they shouldn’t be empty.
Well, I guess the first thing I will try is a new image with no gain or graphs but I doubt either of those are the issue.
And it does seem to be specific to just this feeder. I just change the port on my primary to a non standard port and it works just fine.
Have you tried another port like 8383 
Same results with a few different ports, however, port 420 makes me not care as much. 
What’s the output for:
du -b /usr/share/dump1090-fa/html/jquery/jquery-3.0.0.min.js
Ok loading in chrome with just 8282 it shows jquery-3.0.0.min.js is zero bytes in the dev panel.
Loading http://192.168.25.82:8087/dump1090-fa/ it shows jquery to be 84 kbytes in the dev panel.
However, regardless of how it’s loaded in the browser it shows this on the cmdline.
86341 /usr/share/dump1090-fa/html/jquery/jquery-3.0.0.min.jsI spun up a new image on a 3rd pi and set the port to 8045 without any mods and it works just fine.
I’ll put in gain first and see what happens.
edit - added the html to change gains and no issues.