In several posts I read, that after flashing recovery you should first fully boot into Android, before booting into the new recovery.
I would really like to understand the reason for this.
Anyone who can give some technical details?
You mean the password prompt showing up, though the filesystem has not been encrypted?
Interesting, I thought that happens only, when the TWRP version does not match the bootloader.
Hard to explain, but then weird things happen all the time that cannot always be explained.