Block height = {nothing}

I’ve got 5 Helium miners, 4 of them are fine but one just won’t seem to load any snapshots, block height is always blank, resetting make no difference, what could be the cause?

I had the same thing (US915 variant); firmware was updated from v1.2.8 to v1.2.9 sometime today and it now seems to be working properly. This is discussed more fully in Is this normal - Hotspot info?.