Debugger only starting for projects located in home directory (Ubuntu, QtCreator 3)

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I set a breakpoint in my project and start a debug run. Both gdb and lldb never really launch though.
Somewhere I read a hint, that I should try it with a project placed in the home directory. In that case gdb starts, but runs into the ptrace problem. I then tried it with lldb and execution halted at the breakpoint and I could view variable values.
If lldb works reliable if I place the projects in the home dir, I can live with that. But I'm still curious if this is expected behavior or if I should change anything with my setup.