A month ago, when doing 12man (The Xan), the two subject items dropped quite frequently. Unknown Mixture was often times left on the corpse or went free-for-all, along with the cloth, and the Activation Device dropped every other raid or so. Ever since the patch that upped the drop rate of the Xan Weapon Upgrade (by a ton), I haven't seen a Mixture or Activation Device drop in doing 12man about 5-6 times. Each of those raids there was 1-3 WUs though.
Was something changed (drastically) with the %drop chance of the items in 12man (and, maybe, Vortexx/Mitaar too), such that WUs skyrocketed and Activation Device/Mixture tanked?