Updated LineageOS 15.1 Build
After a long absence, I spent around 15 hours backporting a huge number and variety of security patches to the kernel, testing, and fixing some regressions. I made a new build of LineageOS 15.1 for those who want to use it. It should be quite stable, though I don't know if VoLTE will work - let me know if it does work for you (particularly Indian Jio users). I know many or most of you would have switched to unofficial 16.0 by
@DroidFreak32, but for those who still prefer the smoothness of Oreo over Pie, or want a build that has up to date kernel security patches, here's a build for you.
I still want to bring back official builds, but I haven't decided between Pie and Oreo. Oreo is getting old now, but it runs smoother on these devices than Pie.
https://www.mediafire.com/file/jteq2j9iiw1h64z/lineage-15.1-20190914-UNOFFICIAL-surnia.zip/file
EDIT: There seems to be a race condition in RIL initialization that may cause intermittent issues unless you restart the RIL daemon. I'm working to debug this.
EDIT 2: Hmm... I can't reproduce the problem any more. This build will probably work fine for most then. If the RIL fails to initialize properly for you (no baseband version in Settings->About Phone), please share a logcat from the start of the boot process.
EDIT 3: Another issue with the RIL changes is that netmgrd keeps crashing. Don't rely on this build for a working RIL, I will post a better fixed build tomorrow.