LineageOS / bardockpro / recent LineageOS installation package do not work I have been happily using and occasionally upgrading a bardockpro device for many months.

However, in summer 2019 the device stopped booting into upgrades that were released after July. The most recent build that works, insofar as I know, is the 20190710 nightly build. 

Since then occasionally I tried newer builds - never successfully. I habve also flashed stock rom. and then retried recent lineageos builds. No success.

The problem, in my reading of an issue  is that the device is not critically unlocked. Therefore not all parts can effectively can be flashed.

so, one question was: how to
get 

Device critical unlocked: false


to

Device critical unlocked: true


?

However, my reading of the issue was misleading - and this was not the question. The question was way less specific: how to get the device working with the updated builds?
Well, the solution emerged in a conversation in the German Android-Hilfe. The solution was to 


flash an older Stock ROM version.
let the Stock ROM update itself, and in that process, seemingly, get all the partitions "right".


Afterwards I was able to install recent Lineage OS builds following the standard installation instructions.