Thanks for this thread - I've been having trouble with my RPi 2 and DVBSky S960 since upgrading to LibreELEC 8.0 (green unwatchable mess on most channels, countless continuity errors in tvheadend), but smp's build without media_build seems to be working well for me (media_build was better than 4.9 kernel, but some channels were still bad or only occasionally worked).
However, I'm not sure this problem is RPi-specific. I tried the same setup with my tuner on an x86 laptop (i5-3340M) running LibreELEC 8.0.1 (official build) and was having the exact same problem - it was essentially unusable with the constant continuity errors in TVH, as even the bouquet/mux scan was failing (UK Freesat channels). Let me know if you want me to try any further testing.
It's not pi specific, is the Linux kernel from 4.9 and up. Hopefully is resolved or some lovely person can post an image of the latest generic release with Linux kernel 4.8 (with media)