MrSpock22 I have exactly the same problem, I can not reach a correct focus while using this adapter, and I removed the 5 mm extender.
That adapter is meant to be used with a camera that has a 17.5mm flange focal distance, or 12.5mm flange focal distance when you include the 5mm spacer.
The flange distance for the ASI071 is 17.5mm, so leave the spacer off, and then fine tune the focus by using the nylon T2 spaces that came with the camera adapter -- these go between the adapter and the camera's tilt plate.
If you still have insufficient spacing, places like Agena sells M42/T2 metal washers/spacers, usually up to 1mm thick and as thin as 0.1mm. You may want to choose the metal ones anyway, instead of the flimsy plastic stuff that ZWO provides.
Just try to focus the lens at non-infinity, measure the extra distance you need with a pair of calipers, and add that much spacer.
With many lenses, where all the lens glass elements all move in unison as you focus, you can just leave the focus at the sharpest non-infinity point and not have to deal with spacers. With lenses that moves only some of the glass elements internally, you will need to use precise spacers so that the stars are sharp when the camera lens is at infinity focus -- if not, stars at the edge of the frame won't be sharp when the stars at the center of the frame is sharp ("field flatness").
Chen