Can't restore Nexus 6p Google Drive backup to new LG G6
I had a similar experience with restoring a N6p backup to a Pixel. Nexus was running Oreo and Pixel still on Nougat. After updating Pixel to Oreo and doing a factory reset I was able to restore the N6p backup.

So it seem you can not restore to older Android release, is the LG running older version than the N6p?