How do I get screen captures from VLC to import properly into Premiere?
Looks like a codec that Premiere is unable to read.

I encountered a similar issue with Final Cut when trying to import an MP4 file encoded with H264.  Then came across this advice:  "H.264 is a delivery format, not a production format. You need to convert the media into a suitable format. What that is depends on what the files are and what their frame size is." https://forums.creativecow.net/thread/8/986671

So if you can't recapture with a suitable codec, you'll have to decompress your H264 MP4 file into something Premiere can import.