After upgrading to 15.1 LineageOS seems unable to reboot into recovery (or bootloader).
I posted here, that immediately after installing 20180903 I successfully did both “Advanced reboots” - which was true. This was the first time it did work with 15.1. A week later (September the 10th) it didn’t work. After installing 20180910 it didn’t work. “adb reboot recovery” doesn’t work either.
Is the only reliable way to reboot into recovery a long press of VolUp+Power?