Segmentation Fault when starting Designer

[newgen]

When starting the designer, I suddenly get a segmentation fault and the designer is dead.
Console output:

user@host:~$ designer
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setFont: Painter not active
QPainter::end: Painter not active, aborted
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setFont: Painter not active
QPainter::end: Painter not active, aborted
QPainter::begin: Paint device returned engine == 0, type: 2
...
QPainter::setPen: Painter not active
QPainter::drawRects: Painter not active
QPainter::restore: Unbalanced save/restore
Gleitkomma-Ausnahme (Speicherabzug geschrieben) -> translates to segmentation fault

Any idea what might cause Designer to crash? Qtcreator and my QT app work fine.

System specs:
qttools5-dev-tools - 5.12.8-0ubuntu1
qtcreator - 4.11.0-2build2
Ubuntu focal

Added after 13 minutes:

Other fun fact: I tried to install qt via the official t-unified-linux-x64-4.0.1-online.run. However, the only thing that happens is that is opens a window presumably 10000 pixels wide but without content. I have seen a similar behaviour with VLC, but could not find a solution.

[newgen]

apt-get update+ apt-get upgrade did not solve the problem. Designer is still broken. I am stuck with my software development.

[d_stranz]

Does the Qt maintenance tool exist in the linux distribution? (Don't know - I work in Windows only now). If so, maybe give that a try? Otherwise, you might have to uninstall and reinstall Qt. Sounds like you might have a bad build, configuration, or install.

[stampede]

Is it ubuntu 18 ? some time ago all of sudden the Qt assistant started to crash at startup, I have to start it from the command line with altered "LD_LIBRARY_PATH":

LD_LIBRARY_PATH=/usr/lib/x86_64-linux-gnu assistant &
You might want to double check the library path on your system, I'm on windows laptop now.

I'm not sure why it's needed but it works for me. I won't dig into that, since I'm gonna reinstall the system soon anyway. Please post here when you fix your problem.

[newgen]

Thanks for the feedback and sorry for the delay.

@d_stranz : Never heard of the maintenance tool. Will check it out. Thanks. After several "apt-get update ; apt-get upgrade" I would have assumed the qt libs to be replaced by a newer version that fix hit. However, the segmentation fault remains.

@stampede : Double checked the path. Path looks good. However, the assistant just comes up for a second (only the window frame, no content) and also dies with segmentation fault. My system is still ubuntu focal. I will try to dig in that direction also. Though I am pessimistic as I lack the skill to debug the problem properly.

Btw. I removed the .qt folder in my /home to exclude the possibility of a broken profile or something. No change. Open for suggestions what else to remove.

Added after 5 minutes:

Tried:

apt-get --purge remove libqt5designer5* libqt5designercomponents5* libqwt-headers* libqwt-qt5-dev* qtcreator* qttools5-dev* qttools5-dev-tools*

apt-get install libqt5designer5* libqt5designercomponents5* libqwt-headers* libqwt-qt5-dev* qtcreator* qttools5-dev* qttools5-dev-tools*

Result:
Segmentation fault remains.

Tried to execute designer with root user for a change: Segmentation fault remains.

Added after 5 minutes:

Finally... I created a new ubuntu user and designer works. So, something in my user settings or home seems to crash the designer. Now searching the needle in the haystack.