GLib-GIO-CRITICAL g_menu_insert_item: assertion 'G_IS_MENU (menu)' failed

Hello,

regarding the nextcloud desktop sync client:
The log file .xsession-errors is filled with the following messages:
(nextcloud:144782): GLib-GIO-CRITICAL **: 19:07:30.499: g_menu_insert_item: assertion ‘G_IS_MENU (menu)’ failed
Several thousand lines in bursts when syncinc which produced a formidable 42GB logfile overnight filling my hard drive …

The client works flawlessly otherwise.

Nextcloud-desktop client version 2.6.4-1
Nextcloud-server version 16.0.9
Debian unstable
ii libglib2.0-0:amd64 2.64.2-1
ii libnextcloudsync0:amd64 2.6.4-1
ii libqt5sql5-sqlite:amd64 5.12.5+dfsg-10
ii nextcloud-desktop-common 2.6.4-1
ii libc6:amd64 2.30-4
ii libcompfaceg1 1:1.5.2-5+b2
ii libcloudproviders0:amd64 0.3.0-3
ii libglib2.0-0:amd64 2.64.2-1
ii libglib2.0-0:i386 2.64.2-1
ii libqt5core5a:amd64 5.12.5+dfsg-10
ii libqt5dbus5:amd64 5.12.5+dfsg-10
ii libqt5gui5:amd64 5.12.5+dfsg-10
ii libqt5keychain1:amd64 0.10.0-1
ii libqt5webkit5:amd64 5.212.0~alpha4-1
ii libqt5xml5:amd64 5.12.5+dfsg-10
ii libqt5widgets5:amd64 5.12.5+dfsg-10

How to proceed from here?
Is it possible to turn off warnings/debugging from the client?

Many thanks in advance,
Thomas