On my Zgemma H7S I get the same effect sometimes where it's like the text is missing from the EPG so that multiple EPG entries look blank on the EPG.

I've been experimenting to try and figure out what's going on but I haven't really got very far yet.
I'm hindered by knowing C pretty well but not C++.

I find one thing that makes it go wrong on my Zgemma H7S is if I happen to be flicking through the channels at a time when the EPG is being read (by either OpenTV Zapper or by EPG Refresh).