Unproductive in dissertation research (mathematics/statistics) For my dissertation research, I feel like I was unproductive a lot of times because I didn’t have a good intuition about approaches to even try. I felt as if a whole year was wasted trying ideas that went nowhere. I think the reason for this is because there weren’t many related papers on my dissertation topic so when I’d read papers, I only had a few potential approaches I could think of.

Has anyone else had this problem? I also wish I had another easier/more tractable problem to work on, but my advisor wanted me to focus on this one (generalization bounds based on optimal transport theory).

Now I have some progress, but even now I’m stuck trying to make sense of a function that comes up in my generalization bound. And even that, I’m having a tough time making sense of that even for simple cases. Sometimes I think I’m being unproductive but it’s more because I lack enough relevant ideas than it is sheer laziness. And I also talked about my problem to other professors/researchers but most didn’t have much insight.
Some problems are just hard, and insight can't be scheduled. So, yes, others have had similar problems. Good problems, by the way, are hard to find. They can be too easy and have no real significance. You don't gain much by solving them. Others are just impossible, possibly theoretically, or possibly just at the current state of knowledge. 

My field is different, but one thing I'd probably think of trying if I didn't understand a function would be to model it computationally. Another thing I'd probably want to think about is my partial results. Are they meaningful? Can the be used for other things?

But the best help will probably come from your advisor. If you can explain what is blocking you, maybe the two of you can find a crack to exploit. Just trying to explain your problem and your issue can sometimes free a block, if that is what it is.