Humalog sometimes doing nothing?

I am using a Pendiq 2.0. These do have a good reputation, but perhaps mine is broken?

Anyway, I am observing something very unsettling. Bolus is totally broken for me!

Here is a screenshot:

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Notice that I bolused without any carbs on board. BG decreased as expected, then suddenly a peak that went down, then BG stayed flat!

Just, wtf.

I cannot bolus with this totally weird behavior. What is going on here?