DShow buffer limit

Bit of a strange one and more to do with ffmpeg I think than anything else;

When running a dshow webcam with 1080i5000 screen consumers I run into a buffer limit (regardless of frame rates and video size of the webcam feed)

However seems to run fine when using a 1080p5000 screen consumer.

Any idea why that is the case?

System is an I7 6700 using internal gpu 8gb ram win10