Like the issue some time ago with Soundtoys VST plugins (1) Echoboy show as mono, (2) Soundtoys load as mono, (3) Problem with Soundtoys, Martinic plugins (website) are all loading initially as Mono and not Stereo. Obviously have the workaround to change the Bus Layout can be used but is a bit of a pain as you have to do this in each new Gig.
That is not a Gig Performer issue.
You have the possibility to change the bus layout.
Once you change the bus layout, you can duplicate or copy/paste the desired plugins if you need them multiple times. The bus layout will remain unchanged also when you paste the plugin to the Global rackspace.
Try to use a diffrent plugin format VST2/VST3/AAX… somtimes this works.
But in any case you should contact the plugin maker and report this as a bug.
Already reported to the plugin developer - on Windows they only offer VST2 at present although they are working on the VST3 versions next.