backup stalled if encryption tab opened but not accepted or canceled

[kolAflash]

• I am running an official build of TWRP, downloaded from https://twrp.me/Devices/
• I am running the latest version of TWRP
• I have read the FAQ (https://twrp.me/FAQ/)
• I have searched for my issue and it does not already exist

Device codename: FP3
TWRP version: 3.7.0

WHAT STEPS WILL REPRODUCE THE PROBLEM?

1. open Backup
2. switch to Encryption tab, but don't enter a password or press the "checkmark button" on the keyboard (lower right).
3. switch back to Backup tab without pressing Cancel on Encryption tab
4. start backup

WHAT IS THE EXPECTED RESULT?

Either a backup without encryption, or at least an error message.

WHAT HAPPENS INSTEAD?

Backup starts. But there is no progress (neither files or %).
In background the recovery process is using nearly 100 % CPU. (checked via adb shell top)
But the backup directory stays empty. (waited for > 10 minutes)

ADDITIONAL INFORMATION

/tmp/recovery.log

I:Backup folder set to '/data/media/0/TWRP/BACKUPS/AAAAAAAAAAAA'
Updating partition details...
I:mount -o bind '/data/media/0' '/sdcard' process ended with RC=0
I:Data backup size is 12476MB, free: 21995MB.
I:Unable to mount '/usb-otg'
I:Actual block device: '', current file system: 'auto'
I:Can't probe device /dev/block/mmcblk1
I:Unable to mount '/sd-ext'
I:Actual block device: '/dev/block/mmcblk1', current file system: 'ext4'
...done
I:mount -o bind '/data/media/0' '/sdcard' process ended with RC=0
/data | /dev/block/bootdevice/by-name/userdata | Size: 48871MB Used: 12476MB Free: 21995MB Backup Size: 12476MB
   Flags: Can_Be_Mounted Can_Be_Wiped Can_Be_Backed_Up Wipe_During_Factory_Reset Wipe_Available_in_GUI IsPresent Can_Be_Encrypted Is_Encrypted Is_Decrypted Has_Data_Media Can_Encrypt_Backup Use_Userdata_Encryption Is_Storage Is_Settings_Storage 
   Symlink_Path: /data/media/0
   Symlink_Mount_Point: /sdcard
   Primary_Block_Device: /dev/block/bootdevice/by-name/userdata
   Display_Name: Data
   Storage_Name: Internal Storage
   Backup_Path: /data
   Backup_Name: data
   Backup_Display_Name: Data
   Storage_Path: /data/media/0
   Current_File_System: ext4
   Fstab_File_System: ext4
   Backup_Method: files
   MTP_Storage_ID: 65537

I:Unmounting main partitions...
tw_get_context got selinux context: u:object_r:media_rw_data_file:s0
I:Got default contexts and file mode for storage files.
I:Decrypt adopted storage starting
I:PageManager::LoadFileToBuffer loading filename: '/data/system/storage.xml' directly
I:successfully loaded storage.xml
I:Set page: 'main'
I:Set page: 'clear_vars'
I:Set page: 'main2'
I:operation_end - status=0
I:Set page: 'main'
I:Set page: 'clear_vars'
I:Set page: 'main2'
SELinux contexts loaded from /file_contexts
Full SELinux support is present.
I:Switching packages (TWRP)
I:Copied file /data/recovery/log.gz to /data/recovery/last_log.gz
I:No custom recovery folder found. Using TWRP as default.
I:Attempt to load settings from settings file...
I:InfoManager loading from '/data/media/0/TWRP/.twrps'.
I:No recovery folder found. Using default folder.
I:Backup folder set to '/external_sd/TWRP/BACKUPS/AAAAAAAAAAAA'
I:Copied file /etc/recovery.fstab to /data/recovery/recovery.fstab
I:Version number saved to '/data/recovery/.version'
I:Unable to mount '/usb-otg'
I:Actual block device: '', current file system: 'auto'
I:TWFunc::Set_Brightness: Setting brightness control to 127
I:PageManager::LoadFileToBuffer loading filename: '/twres/languages/de.xml' directly
parsing languageFile
parsing languageFile done
I:Translating partition display names
I:No custom recovery folder found. Using TWRP as default.
I:Backup folder set to '/external_sd/TWRP/BACKUPS/AAAAAAAAAAAA'
I:Starting MTP
I:Cannot find file /sys/class/android_usb/android0/idVendor
I:Cannot find file /sys/class/android_usb/android0/idProduct
I:sending message to add 65537 '/data/media/0' 'Interner Speicher'
I:[MTP] Starting MTP
I:Message sent, add storage ID: 65537 '/data/media/0'
I:sending message to add 65538 '/external_sd' 'Micro SD-Karte'
I:Message sent, add storage ID: 65538 '/external_sd'
MTP aktiviert
I:Check_Lifetime_Writes result: '55589'
I:Starting Adb Backup FIFO
I:App not installed
I:Switching packages (TWRP)
I:Set page: 'main'
I:Set page: 'clear_vars'
I:Set page: 'main2'
I:[MTP] created new mtpserver object
I:[MTP] mtppipe add storage 65537 '/data/media/0'
E:[MTP] Failed to start usb driver!I:[MTP] mtppipe add storage 65538 '/external_sd'
I:Set page: 'install'
I:Set page: 'main'
I:Set page: 'clear_vars'
I:Set page: 'main2'
I:Set page: 'backup'
I:Set overlay: 'select_storage'
I:No custom recovery folder found. Using TWRP as default.
I:Backup folder set to '/data/media/0/TWRP/BACKUPS/AAAAAAAAAAAA'
I:DataManager::SetBackupFolder zip path was /external_sd/Moritz/System/ROMs/Images changing to /sdcard, /external_sd
I:Set overlay: ''
I:Set page: 'clear_vars'
I:Set page: 'backup'
I:Set page: 'backup_options'
I:Set page: 'backupencryption'
I:Set page: 'backup'
I:Set page: 'backup_run'
I:operation_start: 'Nandroid'
Partitions-Informationen werden aktualisiert...
I:Data backup size is 12476MB, free: 21995MB.
I:Unable to mount '/usb-otg'
I:Actual block device: '', current file system: 'auto'
I:Can't probe device /dev/block/mmcblk1
I:Unable to mount '/sd-ext'
I:Actual block device: '/dev/block/mmcblk1', current file system: 'ext4'
...Fertig
I:Backup Name is: '2021-08-09--12-59-37_e_FP3-userdebug_10_BBBBBBBBBBBBB_engroot202'
I:Backup_Folder is: '/data/media/0/TWRP/BACKUPS/AAAAAAAAAAAA/2021-08-09--12-59-37_e_FP3-userdebug_10_BBBBBBBBBBBBB_engroot202'
I:Calculating backup details...
 * Anzahl der zu sichernden Partitionen: 1
 * Gesamtgröße aller Daten: 12476MB
 * Verfügbare Speicherplatz: 21995MB
[SICHERUNG GESTARTET]
 * Ordner für Sicherung: /data/media/0/TWRP/BACKUPS/AAAAAAAAAAAA/2021-08-09--12-59-37_e_FP3-userdebug_10_BBBBBBBBBBBBB_engroot202
Invalid encryption mode 'aes-256-xts:aes-256-cts'
Sichere Data (ohne /data/media)...
Backups of Data do not include any files in internal storage such as pictures or downloads.
Invalid encryption mode 'aes-256-xts:aes-256-cts'
Sicherungs-Datei wird in mehrere Archive aufgeteilt...
I:TWFunc::Set_Brightness: Setting brightness control to 5
I:TWFunc::Set_Brightness: Setting brightness control to 0
I:TWFunc::Set_Brightness: Setting brightness control to 127
I:Set overlay: ''
I:TWFunc::Set_Brightness: Setting brightness control to 0
I:TWFunc::Set_Brightness: Setting brightness control to 127
I:TWFunc::Set_Brightness: Setting brightness control to 5
I:TWFunc::Set_Brightness: Setting brightness control to 0
I:TWFunc::Set_Brightness: Setting brightness control to 127
I:Set overlay: ''
I:TWFunc::Set_Brightness: Setting brightness control to 5
I:TWFunc::Set_Brightness: Setting brightness control to 0
I:TWFunc::Set_Brightness: Setting brightness control to 127
I:Set overlay: ''