I remember some problems with LineageOS 17.1 for LUX if your firmware is from ‘marshmallow’, the solution was you have to install the stock ROM (nougat) first, and then upgrade to custom ROM (Q).
I did this on my LUX and haven’t problems with LineageOS 17.1 and later with /e/OS 0.14q -> 0.15q -> 0.16q
Stock ROM for LUX you can find here :