I am not sure if any other guilds are experiencing this happening, however any time that battle.net decides to reset, (i.e. services go down and come back up), the game gives us approximately 6 Guild Achievements that were obtained forever ago.
- United Nations
- Ambassadors
- Diplomacy
- Dungeon Diplomat
- Pandaren Embassy
- Classic Battles.
This has been happening for us since inception in Shadowlands.
I believed this to be a known issue however after searching, I cannot seem to find anything on this.
This causes major lag and has on occasion, wipes during raid progression or in mythic plus activities.