[xcb] Unknown request in queue while dequeuing

[johndapps]

Received the following messages after a long run of updating files on Google Drive

[xcb] Unknown request in queue while dequeuing
[xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
[xcb] Aborting, sorry about that.
FreeFileSync_x86_64: ../../src/xcb_io.c:163: dequeue_pending_request: Assertion `!xcb_xlib_unknown_req_in_deq' failed.
Aborted (core dumped)

The following was in apport.log

appsj@ubuntu1804:/var/log$ more apport.log
ERROR: apport (pid 867285) Sat May 30 16:40:32 2020: called for pid 750896, sign
al 6, core limit 0, dump mode 1
ERROR: apport (pid 867285) Sat May 30 16:40:32 2020: executable: /home/appsj/Fre
eFileSync/Bin/FreeFileSync_x86_64 (command line "./FreeFileSync_x86_64")
ERROR: apport (pid 867285) Sat May 30 16:40:32 2020: executable does not belong
to a package, ignoring

[Zenju]

Are you able to reproduce the crash or was it a one-off? When exactly did it crash? FreeFileSync doesn't use any graphics functions from worker threads, so "multi-threaded client and XInitThreads has not been called" does not apply.

[johndapps]

Thank you! I'll try and reproduce the error as I know it has happened a few times previously.
What I am sure about is that I was updating from an external drive to a Google drive account. It is a very large transfer with some 65GB and many thousands of f iles.