Finally identified this issue! Anti-squatter script for 1v1 Arenas does not take into account each individual server ID, resulting in significant ELO loss if a player hasn't visited any of the other servers in the past 7 days. For example: If player John visits NA 1v1 Arenas #1 every day, but visited EU 1v1 Arenas but never returns, his ELO will improperly decay on NA 1v1 Arenas #1 every single day. Poss. solutions: Identify every server as the same server ID (lazy, but will sync your ELO between all 1v1 Arenas servers, which is probably the most logical route) Update script to properly decay ELO from each server.