Installing your firmware onto my H4 resolves the error at 116MHz. Now, mind you it took me a few minutes to download the firmware and install it into the VNA. That's all it took to find this problem. The fact the current release has this sort of problem says a lot about the firmware's state.
I mentioned 1.2.14 allows 1.6kHz to 2GHz. v.1.2.08 allows 800Hz to 2.147483647GHz. With the H4 being as old as it is, funny that they can't even settle on something basic like this.
My guess is they expect it increases sales. Like Keysight with their specs for their high end handheld meters. Hams can say, I have a 2GHz antenna analyzer to look at my 2 meter antenna (while connecting Port2 their HTs output).
Similar to I have a Bird meter so I know my readings are perfect.
I have no idea what would have possibly drove the 800Hz. If you could get good data off it, it would be nice to have for PDN measurements.
With the firmware for the original NanoVNA being open source, I guess everyone felt they should start to have a whack at it. The code was very unstable and updated more than Dave's 121GW. Much like the 121GW, it was total hit and miss what would work on each new release. To save me the time of trying to test each version in my search for something stable, I ended up writing a simple automated regression test. While I would expect anyone developing code would have a similar setup, I think the fact that we are seeing this problem with the latest firmware, it continues to be the wild west of coding. Throw something against the wall and see what sticks. Let the end users test our code. It complied without errors, so it's good to go. I didn't change anything that would have effected that... Same old song and dance
To run it against 1.2.08 requires a few changes. I've gone ahead and made those and have it running. It will require several hours to complete but I will upload the report once it is finished. If I had any plans to continue to support the older protocol, I would just start over and include it in my software.