i can produce a working ubtouch install by using the images you have linked from your nextcloud.
i was able to build halium-9.0 from source by emulating some steps in https://gitlab.com/ubports/community-ports/jenkins-ci/halium-build-tools/-/tree/main/ -- if i push the halium-boot.img and vendor.img produced by that build, everything continues working.
if i push the latest android-rootfs.img from Jenkins-CI to /data/, the system also continues working.
if i push the latest vendor.img from Jenkins-CI, with or without the latest android-rootfs.img, the WiFi and Bluetooth break but the system otherwise continues working, including mobile data.
if i flash the latest Jenkins-CI boot.img to that installation, the device will then only boot into the recovery mode. i believe there is a compatibility issue with the "combined" boot image produced here and it might be worth changing the 4th parameter in the Jenkinsfile here to false: https://gitlab.com/ubports/community-ports/jenkins-ci/marlin-sailfish/-/blob/main/Jenkinsfile#L2
i'm still not totally clear on how you are producing the system.imgthat you have in your nextcloud.