Audio/video sync puzzle
I record conferences all the time, so I end up getting 10's of hours of footage at a time. I have a few tricks that help with syncing: 


Run all cams all the time. If a full day shoot gets only 3 files per cam, that's a lot less work to sync than 25 files from each cam. 
Stop and start all cams within the same few seconds. 
Learn to notice key waveforms. Things like applause, audience chatter, and music have unique shapes. You can also watch for "um" and long pauses. 
There's sync tools available, like PluralEyes, that analyze the sound from each clip, then syncs them on the timeline. 
There's time code methods that many pros use, but I've never had any success with them. 


I depend on 1 through 3 almost exclusively. I've gotten very good at reading waveforms and I only stop cams for breaks longer than 10 minutes. All my clips are 30 seconds out of sync at most. It's pretty easy to sync a whole day in 15 minutes. I've used PluralEyes, but found it took too long to process the material, and it was off by about a half second most of the time, so I had to go though and move all the clips anyway. I only use it if I have tons of clips to sync (more than 15), instead of my typical four or five. PluralEyes will get you close, then you have to adjust manually.