Birb_the_II

I had the same issue. Except I tried to do the quest at one point and they did appear. I was not ready for it, so I did some grinding and other quests. When I came back they were gone. The stuff I did between trying the quest and trying a second time was the MIX.R and the rest of the story content. They might be linked together.

I have the exact same issue at this current point though. They did spawn at one point but they no longer do. I've concluded that it's either because i've done the MIX.R or I have completed the story quest.