First, is the film negative or reversal?
If reversal, it might help to repost the entire scene from absolute beginning (lace-up), eliminate some of the middle, uh, sorry stoners, and show the end of scene to roll out.
The Question is: which end is the more light-struck: Heads or tails? (Compare timing).
Before the film was shot, or after?
If negative, examine the head and tail for weird intensity variations at the beginning and end.
If Heads, before you acquired the film, or maybe someone made a little mistake and was afraid to tell you.
Now, if Tails, is heavily light-struck, maybe your friendly Customs official had "just a quick peek-a-boo," or
a "visitor" at the lab was curious. That will never be known... unless someone 'fesses up. (grin).
An anecdote: During the American Revolution an especially gruesome event happened in a tavern. An aspiring psychic was taken to this tavern (early 1970's) to see if this person would respond to the "vibes" and perhaps describe the events that occurred there.
A reporter and I went along and the psychic (in theory, without prior information) came pretty darn close. All well and good.
The reporter flubs repeated stand-ups. On his last flub he becomes so frustrated with himself he blurts "oh, Hell!"
The next one is done perfectly! Now, Back at the station, I am preparing all the films by everyone else for loading the processor.
I start to transfer my 400ft 7242 onto processor reel when up rushes the dimwit newbee with his contribution to that day's TV history. So to facilitate his donation he turns on the light in my locked loading room from outside. Maybe the film will pass thru the door easier with the light on to show the way.
I very strongly encourage him to turn off that light. Things straighten out, and his film was added to the reel.
In short the only piece of raw stock (600--800ft) Light-struck was the busted stand-up my reporter had blurted "Oh Hell."
It started normally then progressed to looking like he was being burned alive ending with white-out at "Oh hell."
Light-strikes are funny things.
Tungsten balanced film: blue goes white first?