MacOS: flash not able to copy custom userdata (Read-only file system error)

[georg90]

I have the following problem when running the flash tool with a customer user-data file:

HOST:~ username$ sudo flash --userdata /Users/username/Desktop/user-data --hostname pi-master https://github.com/hypriot/image-builder-rpi/releases/download/v1.12.3/hypriotos-rpi-v1.12.3.img.zip
Password:
Using cached image /tmp/hypriotos-rpi-v1.12.3.img

Is /dev/disk2 correct? y
Unmounting /dev/disk2 ...
Unmount of all volumes on disk2 was successful
Unmount of all volumes on disk2 was successful
Flashing /tmp/hypriotos-rpi-v1.12.3.img to /dev/rdisk2 ...
1.27GiB 0:00:48 [26.7MiB/s] [======================================================================================================>] 100%            
0+20800 records in
0+20800 records out
1363148800 bytes transferred in 48.675730 secs (28004691 bytes/sec)
Mounting Disk
Mounting /dev/disk2 to customize...
Copying cloud-init /Users/username/Desktop/user-data to /Volumes/HypriotOS/user-data ...
cp: /Volumes/HypriotOS/user-data: Read-only file system

HOST:~ username$ sudo mount -u -w /Volumes/HypriotOS

HOST:~ username$ cp /Users/username/Desktop/user-data /Volumes/HypriotOS/

As you can see when running the flash tool I get a read-only error. I need to manually remount the SD-Card to be able to copy my custom user-data file.

My setup:
MacOS Catalina 10.15.7
flash 2.7.0

Let me know if more info is needed.