It is very difficult to find out.
Copper might be visible on the PCB.
Short on soldering would be most likely between HDMI pins 17 & 18.
Inside the plug is impossible to see.
I though of another possible error: C75 could be shorted or soldered badly.
It is not important for me but for RS/Farnell , I assume (hope) somebody is analyzing the returns and uses the result
to improve the production. After all the production has only just started with about 200-300K out there.
There are still another,million of two to go