Grinder won't let me do moonstone grind at all

Homeworld Remastered Collection Homeworld: Remastered Collection Tech Support
#1

Whenever I try to moonstone grind, the option for moonstone grind does not pop up. I put two legendaries in and a purple gun that I wanted legendary that is purple. The moonstone option does not pop up. I have 120 moonstones.

#2

This is not the borderlands section.

#3
#4

Please try to post in the correct section. Thanks.