I maintain a small portfolio of several hundred images on 500px, which I uploaded couple of years back. Since then I largely forgot about it, because sales were zero. However, several days back, all of a sudden, I got two sales for whooping $12 and $2. What is happening? Have they finally found some clients? Why price is so low? I thought they were selling $49 minimum per image, was it right? Did I miss something? I tried to search forum, but have not found any recent news about 500px.

It looks like a partner sales with low commission. Last days 500px add partner sales for last months to contributors. I got one partner sale yesterday for 0,35 USD 

Your search skills are obviously not very advanced... There are already several recent threads about 500px distributor sales.

Chech sales dates, I got also dozen sales in two days, and on sale page dates are december 2016, march 2017 and so on.
It seems like they are processing license sales for whole year

None for me then.

Though I did bump into one of my pics which seems to have been stolen since I have not sold it.....

Grrrrrrrr.............decent watermark required.......grrrrrrr.......