We also experienced this issue with an QT application. We could track it down to the by default disabled BIG-REQUESTS extension in version 4.1.0.1.
Commenting the line

X2GO_NXAGENT_DEFAULT_OPTIONS+=" -extension BIG-REQUESTS"

in x2goagent.options resolved this issue for us.

Note, that this applies only for new sessions.

Best regards, Jahn