It looks like the reason for dropping observing at 04:53:56 UTC (four seconds before lockloss) was due to the SQZ PMC PZT exceeding its voltage limit, so it unlocked and Guardian attempted to bring things back up. This has happened several times before, where Guardian is usually successful in bringing things back and H1 returns to observing within minutes, so I'm not convinced this is the cause of the lockloss.

However, when looking at Guardian logs around this time, I noticed one of the first things that could indicate a cause for a lockloss was from the IMC_LOCK Guardian, where at 04:54:00 UTC it reported "1st loop is saturated" and opened the ISS second loop. While this process was happening over the course of several milliseconds, the lockloss occurred. Indeed, it seems the drive to the ISS AOM and the secondloop output suddenly dropped right before the first loop opened, but I don't notice a significant change in the diffracted power at this time (see attached screenshot). Unsure as of yet why this would've happened to cause this lockloss.

Other than the ISS, I don't notice any other obvious cause for this lockloss.