Legendary gem locked

I crafted a rank 3 Fervant Fang to use for upgrading my rank 5 Fervant Fang. When I click the “Upgrade” on my rank 5 and then try to add the rank 3, it shows a padlock symbol against the rank 3 and says that it is locked. It has been in this state for 3 days now.

I can find no mention at all in the game or on the support pages about why a gem would be locked or how to unlock it. If I can’t unlock it, all the mats I used to create the Rank 3 Fervant Fang will have been wasted, and I have no way of getting compensated for them.

The Legendary Gem system in DI is already a complete nightmare, to the point where I can see no way of engaging with it (since I am not willing to invest life changing sums of money) and is the number 1 thing most likely to make me stop playing. Seems like they have added things in to make it even worse than I thought.