That looks great! That takes a lot of patience to pull off.
I'd reckon the hard starts may have something to do with the cap and/or ink. I've heard it's better to use period friendly ink with vintage pens. Modern Japanese inks are particularly ill suited to them due to basic pH levels.
Is the hard start with every letter or word? Or just each cap/uncap? If you fill the cap with some water do you see any dripping through the clip or elsewhere? If so the ink will dry up in the nib between uses and cause that hard start. Or it could simply be a threading issue. A lot of modern metal pens have an o-ring to help seal the pen when capped.