I double checked all of the IAS equipment setup: re-leveled everything, made sure all equipment was over the proper monuments, and checked that all required lines were properly sighted (especially important for the Brunson).  With this done I remeasured the pitch and yaw of the ETMy, the results are:

• Pitch: 663 µrad down
• Yaw: 320 µrad CW

The yaw reading is consistent with the one taken yesterday.  The alignment equipment is set up properly, so I think this change in yaw is real and not a result of improperly set up gear; this also means the source of this yaw movement is still unknown.