I have had only a handful of 4K Sales on Videoblocks (Storyblocks) in last 2 years but all of them ended up being refunded. Just yesterday I had two 4K sales both of which got refunded in just 3 minutes. Many other contributers seem to be complaining about the same. Have you ever had a 4K sale there that did not get refunded?
Should I stop uploading 4K clips there?

I have had 4k sales that didn't get refunded. That was last year though.

Only one. But I've only had one 4K sale! No refund.

Two 4K sales, no refunds.

I wouldn't stop uploading 4K. You probably had some bad luck there.

Clearly, someone is building a library to either sell themselves, or give out for free.

I have had a few

Videoblock has never been a big seller for me and I have had two refunds in two years, so nothing bad for me.
Lat month I had a sudden explosion of sales, mostly 4k (probably welcome aboard package, after the rebranding), but not refunds as yet

return is when the sale disappears from the statistics? If so, then this happened to me

Me!

Two or three.

I sold only 1 4K video in more than 3 years there. I have always found this very odd...

I had only one footage sale in storyblock (I started with clips recently)
just few weeks before the sad news of 50\50 commissions.
I got 178$ from that (4k)