At the start of the shift the X & Y Tidal were close to the upper limits, (70,000). Tidal started climbing on 08/30/19 at ~01:58 (08:58) and has been on a sharp uptrend since. Called Hugh, to see what could be done before the inevitable lock loss. Hugh came in and we started looking more in depth for the cause. 

   While Hugh was looking around, I called Peter K. to see if there were issues with the Ref Cav length may have changed. The REF_CAV temperature changed by 0.01K. Could not see anything obviously wrong. (See Plot-1). 

   Plot-2 shows the 5 day trend for the X & Y Tidal signals. There is a marked turn upward at 08/30/19 at 01:59 (08:59), which continues until the upper of 70,000 is reached. One can also still see the tidal sine waveform is clear in the climbing tidal signal. 

   As I was relocking, Hugh continued to look around and found an interesting comparison of the tidal signal and the PSL laser room temperature. Plot-3 is a 30 day trend of the laser room temp and the tidal signal. There is a rise in the tidal associated with three entries into the PSL. Not a smoking gun, but perhaps a clue.      

Time line:    

   IFO broke lock at 08:44 (01:44). Both the Y and X tidal signals had railed at 70,000. 

   Started relocking - At Hugh's suggestion I unlocked ALS-X and ALS-Y to give the tidal a chance to bleed off to zero. 

   09:03 (02:03) Started relocking. Had to tweak ALS-Y a couple of kicks in Yaw to get it to lock.
   09:05 (02:05) Start DRMI_1F
   09:16 (02:16) Drop to ACQUIRE_PRMI - Was not locking so I dressed up PRM Yaw. 
   09:23 (02:23) Back to DRMI_1F
   09:27 (02:27) DRMI_1F locked and continued up the locking trail
                 Stopped at CHECK_AS_SHUTTERS to dress up RF_18 and RF_90 power
                 Made small changes to PRM Pitch and Yaw, No changes to SRM
   09:38 (02:38) Lockloss at ENGAGE_ASC_FOR_FULL_IFO
   09:40 (02:40) Started second relocking
   10:25 (03:25) Relocked at NLN
   10:25 (03:25) No SDF Diffs - Bck to Observing

   10:29 (03:29) Tidal Y = 20885, Tidal X = -445 I will monitor the tidal signals throughout the shift to see if they are climbing again.