Sorry I explained it so poorly, English is not my first language and I'm still struggling sometimes.
I figured out it shows collective amount of material I gathered, that's why I think it was a bug. I was checking both pickup UI and the amout of stone in my toolbar, because my progress was far slower than usually, and there was a difference - I was picking just one stone at a time and the UI showed I should get more.
Today everything seems alright tho. Not sure what happened, but I'll let you know if the issue reappears. Also, thanks for answering, you're doing an amazing job.