Where are all of my SMS messages?

This app is a huge improvement over previous versions, but it still has major glitches. Inexplicably, I cant see SMS messages dated before this past January (but they are visible in Hangout). Id rather just use one app instead of having to rely on both Voice & Hangouts, but all of the features & functions in having a Google phone number cant be achieved in one app.

fruitypoundcake about Google Voice, v2.6