Quite suddenly I have lost motion blur on the video bus. The motion blur line is still showing on the bus and the key points are still there, but motion blur is not happening in the video preview.
What is the problem
There's an icon on the buss that bypasses it and all buss FXs. Have you clicked that my mistake, it's not that easy to see it's active. Be aware it's the same switch that appears in the preview pane, just to really confuse you.
Thankfully I have discovered my oversight.
At some point I had turned the "FX Bypassed" button on in my Video Preview Monitor. Problem is now resolved.