This has started happening recently, so it could be caused by a change in QT or any other library the program depends on.
When loading an existing soundfont, any soundfont, or creating a new one, the program freezes. GDB shows it's stuck in Pile_actions::Maillon::nombreEltRedo().
I haven't been able to get far with this since the code is very confusing to me (I'm not any good with C++).
Could you please tell me what is the version of Arch Linux and Qt libraries? Is there a procedure somewhere to build Polyphone on Arch? I'll try to reproduce the problem and check what is wrong. This appears not to be the first problem linked to a newer version of Qt.
Thank you for these reports, I was able to reproduce the bug. Some classes need to be reworked so I cannot provide you a simple patch or workaround. The next version of Polyphone will fix the problem.