UI freezes when use irrlicht in qt

Question

I use irrlicht to render 3d model (.obj format) in qt 5.5 on ubuntu 18.04, everything works fine, except when I show a qdialog(the qdialog will call:

setWindowFlags(Qt::WindowType::Widget |
            Qt::WindowType::CustomizeWindowHint);
setAttribute(Qt::WA_TranslucentBackground);

if I didn't call the code above, the ui will not be freezed), my whole app ui will be freezed, the qdialog can not be shown, and got lots of warning:

[warning] QXcbConnection: XCB error: 8 (BadMatch), sequence: 6247, resource id: 69206027, major code: 130 (Unknown), minor code: 3.

I search a lot on google, but didn't find a solution, can anybody give me some help? Thanks very much!