Which version do you use?, And where do you get it from?
I get a report that there are some issues with the last version from KXStudio, which may be related to the fftw library it use, which is in turn related to the cabinet.https://sourceforge.net/p/guitarix/bugs/32/#f698
Best would be if you could build guitarix yourself from source, to ensure that it isn't related to the package provided by KXStudio
If, you use the KXStudio version, you should report it falkTX here:https://github.com/KXStudio/Repository/issues
or to the carla bug tracker:https://github.com/falkTX/Carla/issues
As here, the GxAmps and the cabinet works well in Adour4, jalv and Qtractor.
I didn't use Carla, so I cant check if it is a bug in Carla.
As a side note, the cabinet handling in the GxAmps haven't changed in the last Years.