One way to find the blockage point probably best done with 2 people is this: disconnect the hoses at the CAR end, and block each exposed open pipe end with a small bung. In turn, while the other person presses the brake pedal, remove each bung while holding a jar in place to catch the fluid. The fluid should pour out at high rate if the line is clear. Assuming your jar was clean and dry, pour the collected fluid back into the master reservoir, then connect up each of the hoses - JUST the hose, leaving the wheel end of the hose open. Then bung the open end of each hose and repeat the test. At the same time, of course, you can visually inspect each hose joint/coupling for any obvious dirt or swarf.
Once the hoses all check out OK, you can then fit a caliper to each hose - just left hanging loose for now, to make catching the fluid easier. And with no bleed nipple in place. Repeating the test wil confirm the internal oilways within the caliper as being OK.
If this is now OK, then still with the caliper loose for easy handling, fit the bleed niples - again, check visually for any dirt or swarf. If you get any problem now, you know it is with a faulty bleed nipple, or some alignment problem with the bleed nipple seating into the caliper body. Don't forget, errors in manufacturing CAN happen, and in castings like calipers holes can sometimes be drilled incorrectly. It may be, if that's the case, that the most cost-effective remedy is a replacement caliper.
In my experience, obsessive cleanliness when working on brake lines saves a lot of head-scratching over possible blockages.