Silver/Gold Jungler having issues playing champions like Rengar and Kha'Zix

Hey, hi, hello.

I recently came back to the game after a long absence and have taken up jungling with the new preseason. I understand that Rengar and Kha'Zix are both pretty big staples in the current snowbally metagame because they have a good early- and mid-game presence. This also includes champions like Elise and Evelynn. However, I've had a lot of troubles actually playing assassin champions like these in the jungle towards the mid- to late-game despite having relative success in the early game. I've had several games where I've helped my lanes get kills and have had a score line that looks like 2-0-3, but rapidly end up struggling once the enemy team starts grouping. One of the biggest issues I've run into is with teams that have a moderate amount of CC or when the enemy ADC gets fed enough to be able to blow me up before I can do enough damage to blow them up. I feel like I've had much more success with bruiser junglers like Jarvan and Xin Zhao or outright Cinderhulk tanks like Sejuani, Rammus, and Zac who build tankier than champions like Rengar.

My current win rate with Rengar is 13% over 8 games in the last week or so. I'm clearly doing something wrong, but I have no idea what it is.

I've been running what I think are fairly standard rune pages and builds for Rengar; Domination with Electrocute with Precision. Warrior Enchant, usually challenging Smite, into Duskblade and Yomuu's. I just feel like I fall off so hard in the early game and I can't pick someone off unless I have teammate that's able to initiate the fight in a meaningful manner. Even when I get off pretty substantial ganks in the early game, I feel like a fall off. I feel like my pre-6 ganks are mediocre at best unless the enemy is playing way too far forward and gets caught out. I typically take my bot side buff for the good leash, then proceed to do wolves, then take the second buff before taking a scuttle and looking around the map for a gank. If I can't find one, I go back to my jungle and look to farm until something changes or I hit 6 and have a better chance at forcing an encounter.

I don't want to belabor my perspective too much and create an unreadable wall of text. the tl;dr is that I suck with Rengar and I'd love any advice, tips, or videos that I can watch to try and improve my playstyle or see what I'm missing.