Monitor+HRV App: Historical Data Disappears

I have been using the paid version of the Monitor+HRV App by fbbbrown from the IQ Store. 

I have been wondering if there is a way to see a graph of my historical measurements for HRV, pNN50, rMSSD, etc..  So far I have not been able to figure out how to view data for more than a single measurement period, but I think it needs it, to be useful.

My surprise today was that going back even a few days, all the HRV data disappears from the Connect IQ App and only heart rate and irrelevant stuff like distance is retained.  Is this a bug or a "feature?"

Finally, on a different note, how accurate is the HRV data from the optical sensor on a device like the Venu?  Has anyone compared it to an ECG strap?