Hey Wendy,
How frustrating.
Did you do spot check on the file before handing it over?
Always, a good idea to do.
More to the point, the people who showed the file, should have spot-checked whether it was in sync before arrival of the audience.
However, if it’s in sync on your timeline, it should have been in sync on playback file.
Did you render direct to the USB drive?
Are you PC or Mac (Guessing PC, but would be good to know your specs)
You might have thought it finished, but managed to disconnect the drive before the file closed (unlikely, but it does happen).
CBR (Constant Bit Rate) at that kind of size file is always a good place to start.
Maybe also supply a medium size file, in case the system can’t hack it.
Buffering in the background of playing back the file, could potentially be an issue.
When it comes to Digital Cinema, there is a number of places that it can go wrong, including to what kit was between the play-out device, and the projector and speakers.
And, QuickTime player is no more – even Apple has discontinued it.
H264/H265 and/or ProRes is the formats to use these days. Unless you have a format that you prefer and know is working.
Hope that this helps.
Atb
Mads