Hard to tell from your description exactly what is going on, a screen shot would help. If the rPi is not communicating with the HM board the HM home page will load but show no temps... (but the graph wont show temps either)
I'm running a RPI 3b on a 4.3.4 heatermeter and I do get temps showing on the graph, just doesn't display temps at the top in digital form. It also shows when the fan is running