Application terminates after X server session suspended

Recently we've upgraded Qt in our application. Previous version was 5.11.2 built from sources. The new version is precompiled 5.15.2.

After the upgrade an issue started to occur in following scenario: Application is being run on RHEL7 machine accessed with OpenText Exceed TurboX 12.0.4. Then user suspends the ETX session and application terminates with error "The X11 connection broke (error 1). Did the X11 server die?". 

The issue doesn't occur for the version built with Qt 5.11.2 - the app survives the session suspension without trouble.

For Qt 5.11.2 compilation the -qt-xcb flag has been used.

Red Hat machine mentioned above has libxcb 1.13 installed.