M-1 Mac Mini, 16GB, suddenly stuttering with what should be easy footage....

I've been really pleased with the performance of the M-1 mini, with 16GB, but all of a sudden, on a project yesterday, it really started struggling with some pretty simple footage from, of all things, a Mavic Mini 2 drone and a DJI Pocket 2. And then it spilled over into 8 bit footage from a Sony A7c.
It has never struggled with any of this before. The only difference (on some of the footage) is that I had Auto Flicker reduction on in the Pocket 2 and was shooting in Europe, and it output 50fps instead of 60 (I'm using a 24 fps timeline). All the settings (i.e. Better Performance selected instead of Better Quality) are the same as the days before. I've restarted the computer, and the software, but wondered if anyone had any other ideas? Thanks in advance! UPDATE: My bad, the project was set to 4K, not my usual 1080p (still, after all the hoopla, I would have expected the M-1 mini to handle 8bit 4K much better than that:-)

Thanks for the update, Bob! I'm also running a 16GB M1 Mini. That long-GOP compression is really difficult to decode, so I try not to use those files natively on longer-form projects. Keeps me from losing my hair. ;^)

Thanks, Dave. I have gotten lazy, since getting the M-1, just using the 4K 8bit MK4 files right out of my Sony A7c or RX10IV without transcoding when working in a 1080p timeline. But this is a good lesson!

Every December a client brings in footage shot on a drone, GoPro, Osmo or similar odd contraption to be edited. Gave him a price (2019) before the edit and it took forever. It may have been the 60fps frame rate coupled with long GOP or no telling what else but it soured me so on his projects that last year (2020) I doubled the price now knowing what I'd be facing and I explained to him the difficulties and increased time it took to complete his edit.

The point here being no matter how efficient your system some codecs + frame rates + The Great Unknown can be a pain to deal with.