I did notice the value was -1 previously so I found and turned on Auto Compute HFR in the settings. From that point it now reads as zero. I see you also have Quick HFR enabled. I don't. I'll give that a shot.
I just disabled auto compute hfr and checked the graph checkbox and I did get the popup. I don't recall seeing it previously.
Perhaps what you can do in cases where it is not computed is put 'off' in the field.
Re: skyBg, the tool tip popup is clear as to where the data comes from. I'm using SEP Multistar so I am getting values. The values are present if I scan the timeline, just the graph is flat. I figured out why. Turns out my guider was still imaging as the sky brightened, and the tail of it has backgrounds that rapidly increase. If you look at the tail of the graph (way after the last sub so I didn't see it) it does climb rapidly, which shoves the useful stuff down into the floor of the graph. If I delete those lines from the .analyze file the graph is now presenting useful data.