That's right, Laura. No insulin at that preshot.
You can 'stall'; that is, don't feed, and test again later to see if you get a shootable number. (But that may throw your shooting schedule off if you need to wait long enough for that 6.4 to rise to a number you're comfortable shooting at.)
Rupert does seem to throw these occasional low preshots. If you continue to get preshots that are too low too shoot it might be worth considering reducing the dose a tad in hopes that you can arrive at a dose you can shoot consistently, am and pm.
It may be though that some of the high numbers are caused by Rupert dropping low during the insulin cycle, and swinging up high as a response to that (what we call 'bouncing'). Without some mid-cycle data it's not going to be possible to work out the full story.
Does Rupert have any history of ketones at all?
Best wishes,
Eliz