Sync and weird "collisions"

So I've recorded a concert. In part a Panasonic G80 camera at 29,97 fps, and in part with pro audio equipment. Project settings is set to match framerate, resolution etc.

My, apparently naive, idea was to sync the two in Adobe Premiere Elements 2019.

There's also audio from the Panasonic, so I used this to sync by ear. At the beginning it's in perfect sync. But as the hour long concert progress, the video runs ever so slightly faster, and the audio is increasingly out of sync. This is annoying beyond reason, and puzzling, as it's two recordings of the same stretch of time, they should be the same length, and run at the same speed.
So this is the first question: What the hell???

Being the naive person I am, I attempted to cut out single frame lengths of audio here and there to sync it up manually, multiple times in the length of the video. And here the real trouble started; because shifting any clip, be it audio or video, causes random clips down the timeline to jump all over the place, for no apparent reason! They're not linked, they're not touching. But it'll rip it completely to threads, even cut clips into seperate parts and spread them all over the place, for no reason what so ever, other than me having the audacity to move a completely unrelated clip a single frame. And yes, there is space for the clip I'm attempting to move.
So this is my second question: What the actual hell???

I've experienced both before on multiple occations, but never quite this severe. And never found a reason, explanation or actual solution. Any insight would be appreciated.