The volume snapshot driver has completed processing for dismount. Volume GUID: %1 Guidance: When a volume is dismounted, ...

The volume snapshot driver has completed processing for dismount.

Volume GUID: %1

Guidance:
When a volume is dismounted, the volume snapshot driver closes any handles it may have open on the dismounting volume, such as handles to diff areas.  All auto-release snapshots that have diff areas on the dismounting volume are deleted at this time. The volume snapshot driver may also perform some work to detect whether any future direct writes to the volume are to diff area space for persistent snapshots.  If such writes occur this detection work allows the volume snapshot driver to destroy the snapshots, since the direct volume writes may corrupt them.

You should expect this event when a volume dismounts.  No user action is required.