Hi, I'm having the exact same problem on my DaVinci 1.0A flashed with repetier 0.92, I'm trying to run it with a fully up to date raspberrry 3, but the buffer keeps dropping to zero every few seconds, as well as the temperatures keep showing zero ever few seconds, I've tried every baudrate, tried ping pong mode, reflashed my raspberry and my printer but no luck.
What is weird is that on Repetier Host, every thing works fine and the buffer fills correctly, I also tried Octoprint on the raspberry and it works well with no buffer problems on multiple baudrates.