I have the same exact issue you said. Everything looks fine until sleep mode. After that nothing happens for me.... I get the NintendoZone banner but that's as far as I get. You're not alone. (I made an account just for this :/)
I took a look at the rail and noticed that the two last pins were soldered for some reason, luckly I still had the rail of my broken joycon so after I swapped them I was able to use it attached to the console