XPRAサーバーに接続できません

リモートxpraサーバーに接続できないのはなぜですか？

t@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

私のローカルxpraクライアントは

t@ocean:/u/l/jvm$ xpra --version
xpra v3.0.7-r25627

リモートxpra（サーバー、クライアント、またはその両方？）はい

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

ローカルとリモートの両方でLubuntu 18.04を実行しています。

ありがとうございます。