Hmm, that sounds fine. I guess the first thing I'd check would be the connections, and the second would be to put an ammeter in series with your additional load, to verify that it's only pulling what you're expecting. You could also slap a voltmeter at the first junction "North" of the battery and watch the voltage there as you fiddle with things; if your extra load pulls it low enough, it may be triggering "low power, better shut off" electronics in the NH controller.

Regarding all of those LEDs in parallel, sharing a single current-limiting resistor, just a note: the forward voltage of LEDs can vary quite a bit between otherwise identical-looking units, especially the high-powered ones, and especially the white ones. So, the current division between the LEDs may not be as even as you'd expect; the high Vf units might be slacking around, while the low Vf units do the heavy lifting. (The forward voltage also varies with the internal temperature.) I think the Vf can also vary a bit over the life span of the LED, so when possible, folks recommend running them in series and using current instead of voltage regulation. (Though that might be overkill here.)

Best of luck with it,

JAB