Ok, so this question is a bit long and complicated, i will give as much info as possible.
I have tried looking this up for days on end, i have tried every fix possible, that i could find on the intermenets anyway lol
I am developing a game on Google Play and it is already released, but one of the updates was pretty big. the game is about 60mb and the main menu consists of only UI Elements within 3 canvases.
I hope your following 
Here is my issue > My game frame rate on the main menu is really slow, i have alot of UI for all the buttons and textures, here is the main menu and the shop menu.
Ok. So this is what i have tried. I know the default UI shader is terrible for mobile, so i replaced them with either simple mobile shaders and a mixture of pro shaders i got from the asset store, but still no luck.
From looking online i also unticked pixel perfect on all my canvases and still no luck.
Another thing i tried is to dissable other UI elements when clicking on the buy button, using C# and still no luck.
All my textures i have made in low quality max 1k and my graphics settings is on the lowest.
I did try and attach a picture of the profiler but it would not let me. the profiler seems to be telling me its the CPU and is mainly light green.
I have looked on Unity documentation for a bunch of stuff and still nothing.
What have i missed? or what could i have possibly done wrong?
I really need to fix this issue, i have tried everything i can think of so now i have come here to ask the Unity Community. Thank you to everyone who tries to help, its appreciated.