An update how I fixed it:
- Downgrade to fp2-sibon-17.04.0-manual-userdebug.zip via fastboot
- Upgrade to fp2-sibon-17.06.4-ota-userdebug.zip via TWRP.
- Reset userdata: Destroy the LUKS Header for Filesystem Encryption
- Install Apps & Configure
- Encrypt the userdata partition
Status: When listening to audio via vlc (with and without bluetooth) stutter it from time to time.