My current theory is our reward cutoff was too aggressive and rewards were going to far more people than normal.

As is, if your reward proportion for a single rewardable action is <= 0.0001 we don't give you rewards for it. eg if the rewards pool is 100k sats, it needs to be at least 10 sats of rewards to qualify. I think the majority of rewarded actions might've been <10 sats. We should probably lower this threshold because if you have many actions qualifying for 1 sat rewards in a day, they can accumulate to meaningful amounts.