If nethash drops in half then the diff will sooner or later drop in half as well, this is normal.
Same for increase. Thats why I prefer to look at profitability in 24h intervals.
Second line on chart is 24h diff and it's not dropping anywhere. How
estimated_rewards from API is being calculated? Green chart is just this value over time.
If it's based on average 24h block reward and difficulty it cannot suddenly drop 50% and go up 100% in the next half hour, but that's exactly what happens.
I've seen it in another calcs, there it was block reward being detected incorrectly, switches to PoS or MN reward or something like that, and this last block reward value was used for mining reward/profit.
Indeed for aeon there were stats with lower than usual block_reward (around 6).
Thats odd cause the block_reward is fetched straight from the pool.
This happened last time more than 7 days ago. Will be checking this in the future.