Troubleshooting 4k Footage

I'm working on my first project with 4K footage in Davinci Resolve and I'm having a playback speed issue. Half of my footage for the day is playing back in what appears to be slightly slow motion. The weird thing is it's only footage from half the shoot day- clips from the first part of the day play fine. The audio attached to the clip normal speed, and my DP insists he didn't change any settings on the camera. I've tried exporting new proxies from the original footage, as well as starting fresh with a new project to make sure the timeline settings correctly match the clip. I'm at a loss for what to do- has anyone ever experienced this?

Tell us a bit more about that footage and the machine you have, including the GPU.

It's weird that the sound would be normal speed but not the footage...
Is it out of sync ? Does the sound stops before the video ?

Other questions :
1) what camera and codec is the footage from ?
2) does Resolve playback without dropping frames ? (=green dot and framerate above the viewer)

Take a look at the clip info for some footage that works and some that doesn't... make sure that there really isn't something different about them.