Changelog 2017-09-19:

• While the controller is downgrading, it doesn’t upgrade its level even when it has enough progress (progress is not lost, but accumulated without triggering the level up).

I don't understand this. ??

I've noticed something weird with this as well but I'm on shard1. Also I don't know if it's related or not but a day or two ago shard1 tick was at 5.8s avg while shard0 was it's usual 5.3s avg, it slowly went back down to ~2.5 sec eventually.