F10 M5 Rebuilt Engine Not Firing

Hi guys
Hope you are all well
I’ve got an issue which I hope someone may have come across before.

I’ve Bought an F10 M5 with engine damage. I bought a donor engine, stripped that and fully forged it. Used all of the genuine locking tools and used oem gaskets and sealants.
Engine has gone back in and vehicle cranks but will not fire.
only fault code I have listed is for the fan unit which is not fitted at the moment. Other than that, it’s all good.

before putting the engine together I triple checked all timing and went strictly by the workshop manual instructions.
I’ve replaced all 8 injectors and coded them as they were on the donor engine but I reused the original ecu’s which came on the damaged car.

I’ve removed a spark plug per bank with coilpack and checked for spark which is fine
Checking on parameters via diagnostics I have strong rail pressure and the plugs were wet with fuel. So it’s getting fuel. Im
Just confused how you can have spark and fuel but no firing?!

After a big amount of cranking eventually the car started to lock up at points as of it was hydrolocking on its own fuel..? I got a few pops out of the exhaust. If you leave it for a while and attempt again it’s completely fine and turns over without any locking issues.
Compression is perfect aswell.

this Is my first (and last) S63B44 rebuild as I normally stick with buying the s85 V10’s to play around with.
I’ve reset all adaptions and control units and still have no joy. No codes at all to suggest timing or something unplugged.

all help greatly appreciated. Thank you!