I cannot say why there is different data with some files that had ac power source Z= “50 Ohm” vs “50” or “50 Ω”. It’s possible I had converted a Qucs file to QucsStudio using a text editor and a character was corrupted. This is something I have done many times before without issue. I can only assume there is a hidden character I cannot see or QucsStudio is treating Z= “50 Ohm” vs “50” or “50 Ω” differently.
Be aware the QucsStudio Hybrid does not indicate what port in the In/Sum port. Look at the amplitude/phase data for the three “identical” schematics. S31 and S41 are different.