Syndicate Member Hiding?

I'll be the first to admit, I don't fully understand the syndicate stuff. That being said, I'm 19/20 on Defeat Targets III. The last one I need is Rin Yuushu in Research. He is currently a 3* captain in the red square that is Research. I've zoned over and over in Harbour Bridge, as well as run probably 50-100 low tier maps just trying to proc him in to spawning to get that achievement, but he just will not show up.

Are there certain areas I should be looking for him in? Or will he only show up in a certain type of syndicate activity (Jumped vs. escort vs. something else)?

Thanks in advance!!

try high level maps?

Is there a specific tier I should stay above?

Anyone have any ideas? I did run roughly 20, tier 10-12 maps, and no such luck.