The exotic rotator mission Seraph Shield STILL has a softlock where the captain never drops the keycode to unlock the augment terminal before the first "boss room" with the three brigs.
I've noticed that when the shriekers do not spawn, the captain also does not drop the required item.
Just had 3 runs in a row softlock, and with no guarantee the next run won't it is quite off-putting trying to farm patterns.
This has been a bug for as long as the mission has been a rotator but it happens frequently.