Tested my new r2pro and noticed that sdcard was not booted because emmc is not empty. There is a broken bootchain on userpartition which boots till spl uboot and then hang.
Booting from sdcard is only possible if pressing the maskroom button (which i guess should mean maskrom) while poweron.
Then i can erase the beginning of emmc user partition from linux. 2M was not enough so it seems the downstream bootchain is different to mainline where idbloader is at block 64 (32k).
If i erase first 10M i can boot from sdcard.