It seems that heavily trimmed surfaces tend to be lost in translation when they are referenced from an attached model (in the context of a worksession).
Steps as follows :
-Reference said surface in GH
-Detach the file in which this surface lives
-Re-attach the file
-Notice that GH can’t reference it anymore (the orange treatment) , while other referenced surfaces are fine
I tried to whip up an example file with just one of those surfaces, and guess what ? This time it works
Did anyone notice hiccups like these when referencing attached geometry ?