The main jungle problem
It's clear speed.
Not what you'd expect to hear, but after carefully analyzing my games, it's the biggest thing impacting my performance.
Clear speed dramatically increase with items, especially when you're AP. This means if the enemy jungler has a strong jungler that can invade and gets a kill early and gets a clear item, he can overshoot way ahead, because of the low XP you get, he will not only have items and even 2-3 level advantage, while you are stuck with a low clear speed and into a whole, and by the time you exit it, the enemy has 2 dragons and tons of pressure. Same in reverse, you can shut down an enemy jungler if you can fastly clear his jungle, clear yours in a rotation. Without the catch-up XP, clear speed really is important. Sure you can balance it by constant successfully ganking, but that's another topic, since it's not always viable
They need to balance this so that getting an item would not dramatically improve the clear speed and also improve the second jungle spawn clear speed