As a senior developer of 30+ years experience, I agree and was going to post the same thing.

If code is difficult to understand, I consider that to be a bug. And if, for some reason, the section of code actually is difficult to implement, I would at least want a pretty good comment explaining the context around it and the reasons for the approach taken.

Not only will this help improve the code, but if it is a senior developer, it will help them to understand where they've become blind to a particular complexity. It is great feedback to have someone explain that they don't understand code that seems 'fine' to you.