[Gaz64]

You have done just about everything, compression is good, leakdown test is good, spark to all cylinders, swapped spark plugs around etc.

I'd say if you had the intake manifold off, you have a gasket alignment issue on that bank.
The engine then inhales from the crankcase at low throttle angles instead of the intake manifold.

What inlet manifold do you have and what is the firing order please?