The Enertion Hub can be a bit tricky to install perfectly flush. You can see how to install it in this the video using the recommended method https://www.youtube.com/watch?v=K7RKAAMZpLs
The main problem people encounter is due to the size of the M6 bolt, they are a very tight fit, this is actually a good & bad thing. The good thing is it makes the assembly very strong & rigid. During the design phase I considered using smaller M5 bolts, but they just didn't assemble as strong as M6.
The potential issue is that when you screw the M6 bolt into the plastic hub of the wheel it can create its own thread in the plastic. Therefore when the end of the M6 bolt reaches the threaded holes of the aluminium pulley it may get jammed if the thread in the plastic is not perfectly aligned with the thread of the pulley.
The solution to this (which you can see in my video above) is to screw two M6 bolts from the correct side to hold the aluminium pulley flush it place.
Then use the remaining M6 bolts and screw them from the other side, this makes sure the thread that gets cut into the plastic hub is aligned perfectly with the pulley thread. Once you remove the bolts they will screw in perfectly from the correct side.
Alternatively the other solution is to slightly drill out the plastic inside the wheel using a 6mm drill bit, this will prevent the M6 bolt from cutting its own thread into the plastic therefore allowing it to enter the thread of the aluminium pulley freely.