The Stats logging side of things haven't been updated since 2015 so nothing should have changed, I've no control over that and the author hasn't been around for a long time now. I've only made changes to the graphic user interface, which is the part I wrote, neither part is being developed any longer.
Only thing I can think to suggest is to check what various options are set, perhaps it's one of those that creates the extra files.
I think I figured it out; some files are not updated even after checking for updates in the GUI:
HG612_Modem_Stats_Programs-r5.1.zip
Graph6 = 5.1.0.0
Graphpd = 5.1.0.0
HG612 Stats Logging GUI = 5.1.6641.36791
HG612_current_stats = 5.1.0.0
HG612_stats = 5.1.0.0
Modems = 5.1.1.0
SET_HG612_Date_and_Time = 3.0.0.0
HG612_Modem_Stats_Programs-r5.1.0.4.zip
Graph6 = 5.1.0.0
Graphpd = 5.1.0.5
HG612 Stats Logging GUI = 5.1.6641.36791
HG612_current_stats = 5.1.0.1
HG612_stats = 5.1.0.3
Modems = 5.1.1.0
SET_HG612_Date_and_Time = 3.0.0.0
HG612_current_stats 5.1.0.1 produces extra txt files when outputting graphs versus 5.1.0.0 with the same settings.