Looks like a good setup for rf reception, I still do not think that the PID is the problem, otherwise a lot of LG TV sets in TO would be affected.

I still think its an rf overload or multipath issue, I can recall similar thread about a half year ago with different tv tuners. If you can, try to disconnect LG from antenna and run a short piece of RG cable with a 6 inch center conductor exposed as a local antenna and see what happens for chn 5-1. Or buy a cheap indoor antenna and try this result with it.

Good luck

Looked at your rf amp, 8 dB gain with splitting four ways and 17dBmv output, I have to say now, its either multipath OR lack of rf signal at the LG tuner. Have you checked the signal level indicator on the TV? Is it the same as before or similar to chn 19. If the same as rf chn 19 (since 5-1 is on rf chn 20) then the answer is there multipath change due to reflection from a building or weather?