capture cannot keep up

I have been trying to capture hdmi output at 1080p30 and 720p60 on a decklink mini recorder, 8 bit YUV format. In both cases, after about a minute or two I get a dialog box with the following text.

"media express could not capture the clip. one or more frames were dropped."

speed test indicates my disk write speed should be able to handle these and higher rate formats without a problem. 175 MB/s write, 453 MB/s read

I am running windows 10, i7-6700 processor with 24G of memory. Using an SSD (sandisk SD8BAT128G1122) for write.

When i convert to ntsc it keeps up.

Any advice on how to get this to work?

Thanks.