Unsolved Debugging QComboBox delegate freezes System

[gde23]

Hello, I have following problem:
There is a QTreeView that has some delegates set. One of them is a QWidget with some other stuff and a QComboBox on it.
I've connected QComboBox::currentIndexChanged to submit editor data to the model.
Now the problem is, that when I am debugging and the debugger runs into a breakpoint after the QComboBox has been set to a new value my system freezes.
OS is Debian 10 with KDE and Qt is 5.14.2.
Its not completely frozen, so I can restart X by Ctrl+Alt+Print+K, but that is all I can do at this point.

The problem only occurs with the QComboBox, for other delegates everything works normally, so I guess it has to do with the focus staying on the Menu which gets closed or something like that? Any Ideas what could be the reason?