In this instance one of the GPOs contains Windows 2022 settings which are not processed correctly on machines running older OSs.
The merge will not succeed unless the merge is done on a GPOADmin server running on Windows 2022 with a 2022 preferred DC, and a console on a comparable OS level. Without this the settings can be misinterpreted or cause errors at one step of the process or another. GPMC has varying problems with the GPOs when importing depending on the OS of the DC that GPMC is connected to, and the settings in the GPO.
Note that due to how GPMC processed GPOs, a GPO with Windows 2016 specific settings which are not supported in earlier or later OSs will only import correctly on a 2016 DC. Similarly You can only successfully import a GPO and create a correct settings report on a GPO with 2022 specific settings on a 2022 level OS.
If the involved policies contain settings specific to different OS, in the different policies, merging them would not be a great idea, as there is a potential for settings loss on any DC, as the resultant set of settings cannot be imported successfully to a GPO and have a settings report created on any DC.
One additional note here is that the console should not crash if it encounters GPOs in a merge that are not compatible with the currently selected preferred domain controller, as such a defect to handle this situation and present a warning that the GPOs cannot be merged rather than have the console crash was logged
The defect ID: 449127 it will be addressed in a future version of GPOADmin.