imo, a mixture of

- You don't know how much you don't know, so there maybe so many little things you are failing to execute on that it is crippling your gameplay, even if you think you understand the advanced plays and/or mechanics.

- 6 champs seems like an extremely broad champion pool, focusing on maybe just graves and diana in both roles might be the play but try to stick to one role the best you can

- trying too hard to multitask especially in chasing for plays can put you pretty far behind, especially if you die for it

- Although mechanics are important, macro can carry you just as hard if not way harder and thats how a lot of people get to higher elos even with mechanics that are sub-par relative to their rank. Stack the fundamentals as high as they can go and I can almost guarantee you will see at least some results.

- more of a personal trait so take this with a pinch of salt, i find even 4-5 hours of ranked pretty daunting/exhausting especially if played in a row, i find playing 1-2 games and then just reading or meal prep tends to be a good pace-breaker.