Alright well I'm gonna make my suggestion but you don't have to listen. I would switch BACK to aureinand since it definatly was not the problem and cakes has zero advantages including no boot manager like I'm about to suggest.
1. Delete all old cfw files off your sd(cakes,arm9loaderhax.bin,firmware.bin,cetk files or wtv they're called, old boot manager all of it)
2. Download the LATEST [5.1.1 when writing] version of aureinand from her github (
https://github.com/AuroraWright/AuReiNand/releases) and put the arm9loaderhax.bin on root of sd
3. Create a folder called Aurei on the root of sd
4. Create a folder called payloads inside aurei folder
5.place uncart.bin inside payloads folder and rename def_uncart.bin
6.make sure to be holding START BEFORE even pressing power and it should boot( if it doesn't there's a problem with uncart.bin file not the cfw)
7. Never worry about firmware versions and crappy "hacky" ways to gets back arm9 access when you got it on boot instantaneously.
PS: if you follow these direction booting will make the aureinand config menu come up since it will be your "first boot" so check the options you want and shut back down and you'll be setup. Again if it doesn't work you'll have to find a diffrent version of uncart because this is 100% boot rate