project build problems

[WellRedPandit]

This url in .gitmodules

git@github.com:kitsonk/marked.git

causes

Permission denied
fatal: The remote end hung up unexpectedly
Clone of 'git@github.com:kitsonk/marked.git' into submodule path 'src/marked' failed

using git clone without recursive succeeds, but subsequent git submodule init followed by git submodule update causes

git submodule update
Cloning into '_static/Font-Awesome'...
remote: Counting objects: 7261, done.
remote: Compressing objects: 100% (1894/1894), done.
remote: Total 7261 (delta 4148), reused 6617 (delta 3568)
Receiving objects: 100% (7261/7261), 5.83 MiB | 6.19 MiB/s, done.
Resolving deltas: 100% (4148/4148), done.
Submodule path '_static/Font-Awesome': checked out '13d5dd373cbf3f2bddd8ac2ee8df3a1966a62d09'
Cloning into 'refdocs'...
remote: Counting objects: 65, done.
remote: Compressing objects: 100% (27/27), done.
remote: Total 65 (delta 23), reused 65 (delta 23)
Unpacking objects: 100% (65/65), done.
Submodule path 'refdocs': checked out 'cf7a4f155b74bfa735a5255d5e043c139f8d3b6b'
Cloning into 'src/marked'...
remote: Counting objects: 2042, done.
remote: Compressing objects: 100% (957/957), done.
remote: Total 2042 (delta 913), reused 1813 (delta 704)
Receiving objects: 100% (2042/2042), 341.24 KiB | 340 KiB/s, done.
Resolving deltas: 100% (913/913), done.
fatal: reference is not a tree: 55aa5f9ebd626c844a841c26b54e61f395c76fd4
Cloning into 'src/util'...
remote: Counting objects: 8019, done.
remote: Compressing objects: 100% (2458/2458), done.
remote: Total 8019 (delta 5363), reused 7958 (delta 5312)
Receiving objects: 100% (8019/8019), 79.39 MiB | 6.64 MiB/s, done.
Resolving deltas: 100% (5363/5363), done.
fatal: reference is not a tree: 57bdb06edefddf1fcbc0d4a072c5c5b96b9f2950
Unable to checkout '55aa5f9ebd626c844a841c26b54e61f395c76fd4' in submodule path 'src/marked'
Unable to checkout '57bdb06edefddf1fcbc0d4a072c5c5b96b9f2950' in submodule path 'src/util'