Won't pick up blocks

I was trying to get some more wood, and when I broke the tree down it was all like normal. The thing was, I noticed it wasn't in my inventory. And when I looked at the tree, there were the blocks which I had to collect. I kept trying to get them- walk through the it, near it, past it. I just couldn't collect it!! So I thought ok I'll just craft something and come back later. So I crafted some wooden planks and the same thing happens! I couldn't collect them!!

I have found that if you are holding wood and you are trying to collect wood, then it will happen like normal. But I didn't have any wooden planks so I can't collect