@dimka The answer is simple, LineageOS is a modded Android, Ubuntu Touch is totally different: Different kernel config, different use of partitions, different structure of the initramfs etc.
So, that all makes it hard to cover every case that users might have depending on:
if they repartitioned their device if there is still data in the system partition which will prevent correct boot if data has been encrypted if the vendor partition is from a different Android releaseAnd more ^^