I have a Legion Pro 5i 16IRX8. The keyboard backlighting doesn't work, the ports on the right side don't work (only the e-privacy shutter) and it lags. Badly.
I've already done most suggestions (wiping and reinstalling Vantage, reinstalling the gaming feature, reinstalling drivers, DC drain and more).
It began happening after a screen replacement at a local shop (I broke it playing FC25 because I raged. The keyboard lights, ports and all of that were still working perfectly though)
I did install the new BIOS update (v11 I think it's called) and the Dolby Vision kit from Lenovo's website (in addition to trying to reinstall drivers that I think are at fault).