gpu visualizer Scene bar not full?

It never happened to me, first time a see this: the Scene bar in the GPU visualizer is not full, but since it is a proportional representation of the time used by each step, how can it be?

Shouldn’t it be always full for any frame analyzed?

Even if it’s not a bug or an issue, what does this mean? How am i supposed to interpret the data?

p.s.: the analyzer has been called during a 32fps execution of a vr project at r.ScreenPercentage=400 and gpu utilization of almost 100% (with a pair of gtx 1080) according to nvidia-smi tool, so the gpus are not underburdened.