(edited by Abriel.4103)
Lost progress/Item after maintenance.
Same thing happened to me except with a heart event. Before the maintenance I had finished roughly 80% of a heart, killing enemies to complete it and getting their drops. After maintenance, it was back down to 20% and most of the drops were gone. No big deal in my case, but a curiosity to be sure, especially if it can also effect things like dungeon runs or, say, higher-end chest drops.
I certainly know not to mess around too seriously close to maintenance time until this is resolved.