[winswitch] Fail to connect to a XPRA server

[Tim]

Why can't I connect to the remote xpra server? 

    t at ocean:/u/l/jvm$ xpra shadow ssh:"onion":0
    
    (xpra:24602): dbind-WARNING **: 21:28:35.326: Couldn't register with accessibility bus: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.
    2020-04-06 21:28:35,442 Xpra GTK3 X11 client version 3.0.7-r25627 64-bit
    2020-04-06 21:28:35,721  running on Linux Ubuntu 18.04 bionic
    2020-04-06 21:28:35,724  window manager is 'Openbox'
    2020-04-06 21:28:35,770 Warning: failed to import opencv:
    2020-04-06 21:28:35,770  No module named 'cv2'
    2020-04-06 21:28:35,770  webcam forwarding is disabled
    
    (Xpra-Audio-query:24619): dbind-WARNING **: 21:28:36.798: Couldn't register with accessibility bus: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.
    2020-04-06 21:28:36,926 GStreamer version 1.14.5 for Python 3.6.9 64-bit
    2020-04-06 21:28:37,314 No OpenGL_accelerate module loaded: No module named 'OpenGL_accelerate'
    2020-04-06 21:28:37,772 Error: cannot handle window transparency
    2020-04-06 21:28:37,772  screen is not composited
    2020-04-06 21:28:37,848 Warning: vendor 'Intel Open Source Technology Center' is greylisted,
    2020-04-06 21:28:37,848  you may want to turn off OpenGL if you encounter bugs
    2020-04-06 21:28:38,043 Error: cannot handle window transparency
    2020-04-06 21:28:38,043  screen is not composited
    2020-04-06 21:28:38,053 Warning: window 4294967295 changed its transparency attribute
    2020-04-06 21:28:38,054  from False to True, behaviour is undefined
    2020-04-06 21:28:38,133 OpenGL enabled with Mesa DRI Mobile Intel® GM45 Express Chipset
    2020-04-06 21:28:38,407 Connected (version 2.0, client OpenSSH_7.6p1)
    2020-04-06 21:28:38,961 loaded RSA private key from '/home/t/.ssh/id_rsa'
    2020-04-06 21:28:38,981 Authentication (publickey) successful!
    2020-04-06 21:28:39,275  keyboard settings: rules=evdev, model=pc105, layout=us
    2020-04-06 21:28:39,356  desktop size is 1440x900 with 1 screen:
    2020-04-06 21:28:39,356   :0.0 (381x238 mm - DPI: 96x96) workarea: 1440x876
    2020-04-06 21:28:39,357     LVDS-1 (303x190 mm - DPI: 120x120)
    2020-04-06 21:28:39,432 no ethtool interface speed available for wlx801f02b5c389
    ^C
    2020-04-06 21:28:55,157 got signal SIGINT
    2020-04-06 21:28:55,157 exiting

My local xpra client is

    t at ocean:/u/l/jvm$ xpra --version
    xpra v3.0.7-r25627
    
A remote xpra (server, or client or both?) is

    t at ocean:/u/l/jvm$ ssh t at onion
    t at onion:~$ xpra --version
    xpra v3.0.8-r25889
    t at onion:~$ logout
    Connection to onion closed.

Both local and remote are running Lubuntu 18.04.
   
Thanks.