Hi Barak,
I hope you were able to solve the issue by now. Just in case you are still struggling, I would need to know a bit more about your setup, the Squish package you are using, and the Qt libraries used by your application.
First of all, you need to ensure that you are using a Squish package that is compatible your your application:
https://doc.qt.io/squish/installing-from-binary-packages.html#choosing-the-correct-squish-package
If you think that you choose the right one but the problem still occurs, please share the squishserver logs generated after you start the application under test via Squish.