Just yesterday I was seeing normal opponents (i.e. wood league banner parts and partial Mastery level progression), but all of a sudden starting this morning, for 17 battles in a row until I lost, all my opponents had gold, platinum, diamond etc. banners (which won't be available for a few weeks at least; stone will be available in a few hours).
Stats breakdown:
Wood (Green): 0
Stone (Yellow): 3
Silver (Orange): 5
Gold (Sky Blue): 1
Platinum (Purple): 5
Diamond (Red): 3
With battles already pretty stacked against you, Rovio turning a blind eye to these Android APK hacks is unfortunate. One common sign of these hacked teams is that the all 3 birds' Mastery progress bar has no partial fill, so they're all exactly Level # mastery.
Is anyone still getting wood or stone banner opponents? My encounter rate of legit teams right now is 0%...
Some screenshots of the encounters in order of appearance: