At the start of Cardano epoch 234 on December 6th, we updated a network parameter that may have affected your rewards.
We increased the k parameter - which affects the 'optimal' number of pools in the Cardano network - from 150 to 500. This change lowered the saturation point for stake pools from 220 million to just under 64 million, which means you could be missing out on some rewards if you stayed in an oversaturated pool.
Oversaturated pools earn lower rewards than pools below the saturation limit. If you are currently delegating to a stake pool that is over 30% saturation, If you have not done so already, you may want to redelegate your ada to a less saturated pool to avoid missing out on rewards.
To learn more about k, please read our blog post: Parameters and decentralization: the way ahead
You may also find this video useful: Delegating ADA