Maybe I’ve found the bug in the original config file. Can you try raspberrypi4_ubuntu_config again after applying this patch?
diff --git a/configs/raspberrypi4_ubuntu_config b/configs/raspberrypi4_ubuntu_config
index 2d0b7a5..9708f5e 100644
--- a/configs/raspberrypi4_ubuntu_config
+++ b/configs/raspberrypi4_ubuntu_config
@@ -1,7 +1,4 @@
-# Binaries generated with the following script:
-#
-# https://github.com/drewmoseley/mender-convert-integration-scripts/blob/master/build-uboot-rpi.shraspberrypi-integration-scripts.tar.gz
-RASPBERRYPI_BINARIES="raspberrypi4-integration-2019.01.tar.gz"
+RASPBERRYPI_CONFIG="raspberrypi4"
RASPBERRYPI_KERNEL_IMAGE="vmlinuz"
MENDER_KERNEL_IMAGETYPE="zImage"
MENDER_DEVICE_TYPE="raspberrypi4"