Hey man.
I notice that outside of your combos, your draw spells tend to be one shots. Maybe including more repeatable draw options would help?
You've already got Arcanis in your sideboard, which works well with all the untap synergies you have anyway, but triple blue might not be ideal for a 3 colour deck.
Similarly
Necropotence could do a lot of work, but triple black could have the same option. Also,
Bolas's Citadel offers serious card advantage, especially with your cheap spells, but again, triple black isn't ideal.
One of my personal favourite repeatable draw options is
Greed. Both the casting cost and activation cost are easy enough for a 3 colour deck, and if you're assembling a game winning combo, the loss of life means next to nothing. Also, it has sick art. Especially the print with the dude vomiting coins.
I also love
Kefnet the Mindful, but I recognise that he isn't amazing and I have a fair amount of personal bias. An indestructible, 3cmc mana sync that draws cards isn't nothing, and in my personal
experience, having a 5/5 indestructible flyer is often worth keeping a card in hand for an extra turn.
Anyway, I think a source of repeatable card draw could potentially help with the issues you've been having. I hope it works out for you man. Let us know how it goes.