No entries for me either for the HD channels (Mendip transmitter), or at least very few.
Using OSMC on a Raspberry Pi 3 with TV Headend Add-on, which gives me version 4.2.4.
Maybe an update will fix it but in the meantime, this is my workaround:
From the web interface, go to Configuration -> Channel / EPG -> Channels. For each HD channel click Edit, then View Level: Expert. Set 'Reuse EPG from:' to the equivalent SD channel - for BBC ONE HD, choose BBC ONE West, etc.
Then on the EPG Grabber tag, click 'Trigger OTA EPG Grabber', then 'Re-run internal EPG Grabbers'.
Restart the Raspberry Pi.
Then you should have the EPG entries for the SD Channels populating the HD Channels guide. Close enough.