mo123 I have now pushed minor updates to my rockchip-part7 branch, mainly contains device tree tuning, fix for wifi on rockbox and initial bluetooth support on box-trn9.
The use of uart2 for BT on the MVR9 seems to cause a freeze on reboot, enable BT by adding a bluetooth bootarg to extlinux.conf
I belive I have found the issue with bluetooth on MVR9, the trn9 schematics shows that uart2/ttyS2 is used for bluetooth and the hciattach-realtek.service is tyring to initialize it using uart0/ttyS0.
You can try to cp /usr/lib/systemd/system/hciattach-realtek.service /storage/.config/system.d/ and change ttyS0 to ttyS2 and restart the box to see if bluetooth starts working.
The change to ttyS2 is also needed isn't it?