I just did an TW update 20200701->20200721 (on two machines)

After this update, I cannot connect to a running X server on the updated
machine anymore.  I use x11vnc_ssh for this, i.e.:

woodstock:~% x11vnc_ssh astro@astro1

(woodstock and astro1 are the two 0721 machines).  I get an error right away

Invalid MIT-MAGIC-COOKIE-1 keyInvalid MIT-MAGIC-COOKIE-1 key25/07/2020 21:21:45
XOpenDisplay(":0") failed.
25/07/2020 21:21:45 Trying again with XAUTHLOCALHOSTNAME=localhost ...
Invalid MIT-MAGIC-COOKIE-1 keyNo protocol specified
25/07/2020 21:21:45 XOpenDisplay(":0") failed.
25/07/2020 21:21:45 Trying again with unset XAUTHLOCALHOSTNAME ...
Invalid MIT-MAGIC-COOKIE-1 keyNo protocol specified

25/07/2020 21:21:45 ***************************************
25/07/2020 21:21:45 *** XOpenDisplay failed (:0)

It has been working before the update without any problems, and I can still
connect that way to both another TW machine still running 20200701 or some old
Leap 42.3 computers.  So it seems something has changed on the server side.  
0701 has x11vnc-0.9.16-2.1, 0721 has x11vnc-0.9.16-2.2, so it was only
recompiled...