ConnectCore 6UL SBC SWU Update broken with 4.0


I tried to migrate our system image for the CC 6UL SBC Pro from 3.2 to 4.0, which worked fine, but updating the software (between 4.0 versions) with *.swu packages seems broken:

[RECOVERY] Starting recovery...
to back
[RECOVERY] Checking update package 'core-image-base-swu-ccimx6ulsbc-20230308072651.swu'
[ERROR] : SWUPDATE failed [0] ERROR : HW compatibility not found
[ERROR] : SWUPDATE failed [0] ERROR : Found nothing to install
[ERROR] : SWUPDATE failed [0] ERROR : no parser available to parse sw-description!
[ERROR] : SWUPDATE failed [0] ERROR : Compatible SW not found
swupdate_image_write failed: Connection reset by peer
[ERROR] : SWUPDATE failed [0] ERROR : SWUpdate *failed* ! must be installed for pthread_exit to work
[RECOVERY] [ERROR] Invalid update package 'core-image-base-swu-ccimx6ulsbc-20230308072651.swu'
[RECOVERY] The system will now reboot in 10 seconds

Our systems is mainly based on core-image-base with small changes to the kernel and some additional packages.

Any ideas what could be wrong?

kind regards