I locked the PRMI, and tried to turn on the ASS, but this caused PRMI to lose lock.
Since this is similar to what happened the other night (see elog 9243, 2nd big paragraph), I looked into it a little further. I noticed that the POP QPD pitch was very close to the edge of the QPD, so I went out and (while PRMI was locked) recentered the POP QPD. After doing so, I was able to run the PRM ASS, and it worked very nicely, just as it has before. So, it looks like something drifted, such that the optimal PRM alignment caused the POP beam to not be fully on the QPD. Since the ASC loop is triggered by PRMI lock, and is constantly on, falling off the QPD causes lockloss.
While I was out there, I tweaked up the PMC pitch alignment yet again. The FSS numbers all looked reasonable, however PMC transmission was ~0.75 . I did a tiny bit of work in pitch, and now we're back to 0.83 transmission.