It could be a procedure problem than an actual thread problem. Ideally the threads would be perfect but that's really never the case.

It will almost always cause some fussing around if you install the drive side all the way first on a cartridge BB. Try installing the non-drive side first, that way you can rule out any threading issues. Next back the non-drive side off half way and install the drive side, now you can see if it's a misalignment between the two sides.