This morning the IFO was locked on RF while I was taking some OMC scans.  The SRC cavity alignment started to drift so I turned off the SRC1Y loop and manually aligned it.  A few minutes later we lost lock.  Apparently what happened was that SR3 started drfiting quickly. 

Now it's position has changed by a few 100 urad according to the osems, although the oplev says it hasn't moved.  We still see a beam at the AS port, so the osems must be wrong.  The optic is moving around a lot (10s of urad) according to the osems and the oplev, and the beam is moving wildly on the AS camera.  

I took the suspension guardian to "safe" and according to the optical lever the motion has quieted down to less than 1 urad, while the osems still see large glitches.  

I will attach some plots once I have made some that are easier to read, but this seems like a problem with osems electonics. 

Edit to add: LF and RT osems seem to be the problem, as the optic has calmed down with the suspension in safe those two osems are still seeing large glitches. (first attachment)

Second attachment shows what happened at the time of the lockloss.