So everything basically still works on 14.1 except that this prompt is annoying? Now I understood the message. Will report upstream.
EDIT: Use https://paste.omnirom.org/ and upload /tmp/recovery.log and the output of dmesg - the issue template wants this 
For 15.1 the problem is reported in https://github.com/omnirom/android_bootable_recovery/issues/224 - can you check if the log listed in the issue is the same as on the device in /tmp/recovery.log?
For the 14.1 stuff I can do the logs when I’m back on 14.1.
As for 15.1 …
The few lines listed there under ADDITIONAL INFORMATION are not the recovery.log, but the TWRP console (?) output you can view with the button at the bottom right.
For Screen Lock in LineageOS 15.1 set to “None” it reads:
Failed to decrypt data.
Unable to decrypt with default password. You may need to perform a Format Data.
Updating partition details...
...done
Unable to mount storage
Full SELinux support is present.
At this point TWRP prompts for a decryption password, but there is none. Every attempt to enter one adds the following line to the output:
Failed to decrypt data.
For Screen Lock set to an actual lock (pattern/ PIN/ password) it reads
Updating partition details...
...done
Unable to mount storage
Full SELinux support is present.
At this point TWRP prompts for the decryption pattern/ password (TWRP doesn’t distinguish between PIN and password with this prompt, worked with PINs nonetheless in the past).
Every attempt to decrypt with the pattern/ PIN/ password given by the user adds the following line to the output:
Failed to decrypt data.
recovery.log for Screen Lock set to “None” … Edit: is on GitHub.
recovery.log for Screen Lock set to an actual lock … Edit: is on GitHub.
Sorry, I can’t really help there… Maybe put it into the issue I linked above…
Have done so.
TWRP 3.2.2-0 recovery.log: https://paste.omnirom.org/view/d0991ad4
TWRP 3.2.2-0 dmesg.log: https://paste.omnirom.org/view/e2fd6fc4
And I can confirm: TWRP 3.2.1-0 works for the LineageOS 14.1 Updater and encrypted data.
(Yay, I used the Updater for the first time .)
I noticed TWRP 3.2.1-0 also doesn’t automatically install OTA updates if it has to present the “Keep Read Only” prompt first.
So this prompt seems to break the OTA installation, encrypted data “only” triggers the prompt.
Please add your comments to the issue if they are of interest to it. I won’t copy-paste them there 
I copy-pasted them here .
As far as I get it, the solution to the Problem here is either
Am I right?
I’m on the same page.
Yes.
And if you want to have the automatic install feature working, boot into TWRP 3.2.1-0 after installing it and enable “Never show this screen during boot again” at the Keep Read Only prompt.
Back to TWRP 3.2.1. Since I didn’t have any problems with that version I’m fine with it.
After updating to the lastest LOS version, I can confirm that the problem must be included in the last update. With TWRP 3.2.1-0 the update went like a charm.
TWRP 3.2.3 is released:
https://twrp.me/site/update/2018/08/06/twrp-3.2.3-0-released.html
I’m not sure if it belongs in this topic, but I have the problem that I can’t enter anymore the recovery mode.
Last week I did the upgrade to LOS 15.1 and wanted to update to this weeks update of LOS today, but couldn’t install anything because it seems like I can’t enter TWRP anymore? Afterwards the failed update, my FP2 simply rebooted instead of enter the recovery mode, so I tried to reboot into recovery without the LOS updater app, but even this didn’t work.
So I’m not sure what is wrong? Do I need to reflash TWRP or did I brick something?
In LOS everything seems to work, at least I didn’t imagine anything wrong.
before the update to 15.1 I installed the latest version of TWRP.
@Roboe, @z3ntu, @AnotherElk: any ideas?
Please confirm … if you press Vol + all the way through rebooting (from the moment the screen goes blank to the moment TWRP appears) … this doesn’t work?
If in doubt, you can do this anytime.
Well, there’s always booting TWRP without flashing it …
Hi @AnotherElk
the guide to boot into recovery without flashing doesn’t work for me, because similar to @bastoGrande my phone after flashing last weeks’ LOS 15.1 can now only reboot into OS.
Any adb reboot recovery or adb reboot bootloader (or power + Vol+ or power + Vol-) always results into booting OS instead. Even when using the previously installed TWRP app I experience the same problem.
fastboot doesn’t recognize the phone when OS has booted and with adb I cannot flash anything…
The guide doesn’t do anything with ADB.
Please follow the guide (resulting in … fastboot boot signed_recovery_image_of_choice).
Juhuu, that worked already… afterwards I entered TWRP I installed the LOS-update right away, but what is the problem? Is it a known issue? Do I need to change something?