[Android Software Development] rptb1:
No improvement, but the system now seems to boot up to a blank screen rather than immediately shutting down. I can press the power button and get a "power off" / "reboot" menu, but nothing else appears.

"adb logcat" produces >25000 lines on the first boot, with >2000 lines of error, distributed like this:

rb@bluejay$ sed -ne 's/^.* [0-9][0-9]* E \([A-Za-z]*\):.*$/\1/p' < logcat-2018-09-23-20-19.txt | sort | uniq -c | sort -nr | head
1386 AndroidRuntime
213 InputDispatcher
142 libmdmdetect
52 RankingHelper
41 OMXNodeInstance
28 ActivityManager
23 WifiVendorHal
19 SystemServiceRegistry
17 JniUtils
11 BatteryExternalStatsWorker

A lot of these seem to do with "keyguard", which this StackExchange post says is to do with the lockscreen.

rb@bluejay:~/Downloads/FP2$ grep -i keyguard logcat-2018-09-23-20-19.txt | wc -l
1331

So I restored to my last Lineage OS backup, disabled the lock screen, wiped, and tried again. No better.

There are many many errors like this:

09-23 11:22:56.023 4810 4810 E AndroidRuntime: FATAL EXCEPTION: main
09-23 11:22:56.023 4810 4810 E AndroidRuntime: Process: com.android.systemui, PID: 4810
09-23 11:22:56.023 4810 4810 E AndroidRuntime: java.lang.RuntimeException: Unable to create service com.android.systemui.SystemUIService: java.lang.NullPointerException: Attempt to invoke interface method 'void android.service.vr.IVrManager.registerListener(android.service.vr.IVrStateCallbacks)' on a null object reference
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at android.app.ActivityThread.handleCreateService(ActivityThread.java:3349)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at android.app.ActivityThread.-wrap4(Unknown Source:0)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1677)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at android.os.Handler.dispatchMessage(Handler.java:106)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at android.os.Looper.loop(Looper.java:164)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at android.app.ActivityThread.main(ActivityThread.java:6494)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at java.lang.reflect.Method.invoke(Native Method)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:440)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
09-23 11:22:56.023 4810 4810 E AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'void android.service.vr.IVrManager.registerListener(android.service.vr.IVrStateCallbacks)' on a null object reference
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at com.android.systemui.statusbar.phone.StatusBar.start(StatusBar.java:1050)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at com.android.systemui.SystemBars.createStatusBarFromConfig(SystemBars.java:71)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at com.android.systemui.SystemBars.start(SystemBars.java:42)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at com.android.systemui.SystemUIApplication.startServicesIfNeeded(SystemUIApplication.java:215)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at com.android.systemui.SystemUIApplication.startServicesIfNeeded(SystemUIApplication.java:164)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at com.android.systemui.SystemUIService.onCreate(SystemUIService.java:33)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	at android.app.ActivityThread.handleCreateService(ActivityThread.java:3339)
09-23 11:22:56.023 4810 4810 E AndroidRuntime:	... 8 more