I think I see what you mean.
The glide path diamond first appeared shortly before ABEVE at 6200 feet.
I set my VNAV altitude to 4000 ft to match the final approach fix constraint at UMUXE and was letting it descend.
I activated approach shortly after ZICZU while I was still below the glide path diamond and at 4200 ft. The diamond turned solid magenta and I picked up the GP appropriately a short time later.
However, I still had VNAV armed, because once it hit my VNAV top-of-descent point, VNAV PATH activated, approach de-activated, and it started to follow the VNAV path to 4000 ft. If I would have done nothing, it would have leveled off at 4000 ft. and stayed there since approach was off.
I turned off VNAV and re-armed approach and it caught the GP and took me down OK.
This does seem to be an odd quirk of such a small change from 4200 ft to 4000 ft. I guess the moral of the story is turn off VNAV once you’ve armed the approach?
EDIT: Looks like this has also been reported in the main NXi thread here: Working Title G1000 NXi Discussion Thread - #2768 by CriticalClub72
