Bluetooth rfcomm listen doesn't work

Using yellow_wp77xx_0.6.0.spk. On the mangOH yellow I run rfcomm listen:

root@swi-mdm9x28-wp:~# bluetoothctl
Agent registered
[CHG] Controller 3C:E1:A1:E8:B6:E1 Pairable: yes
[bluetooth]# power on
Changing power on succeeded
[CHG] Controller 3C:E1:A1:E8:B6:E1 Powered: yes
[bluetooth]# discoverable on
Changing discoverable on succeeded
[CHG] Controller 3C:E1:A1:E8:B6:E1 Discoverable: yes
[bluetooth]# exit
root@swi-mdm9x28-wp:~# rfcomm listen /dev/rfcomm0
Waiting for connection on channel 1

Initiate a connection from Ubuntu:

paul@paul-ThinkCentre-M72e:~$ sudo rfcomm connect /dev/rfcomm0 3C:E1:A1:E8:B6:E1[sudo] password for paul: 
Connected /dev/rfcomm0 to 3C:E1:A1:E8:B6:E1 on channel 1
Press CTRL-C for hangup

But the mangOH side just hangs. It’s supposed to indicate the incoming connection. Control-C does not terminate the rfcomm listen. The connection stays up until terminated on the Ubuntu side (mangOH still hangs) or the mangOH is rebooted.