FileDialog not rendering after porting from 5.9 to 5.12

[rigu10]

Hello, i'm working on porting a qt/qml project from version 5.9 to 5.12 on RedHat 7. I have a FileDialog that works fine, until i open a new tab where i have a QQuickPaintedItem to render. At this point any FileDialog in the code doesn't show up anymore (it seems that it doesn't get rendered). I tried to comment the function that renders the QQuickPaintedItem and i have no issue with the FileDialog. Any idea on what changed between the two version of Qt that makes this redering so problematic?
I also tried the code on Windows 10 and i don't have this issue.
p.s. with 5.9 i never had this issue
Thanks in advance