Please describe the problem.

As originally reported in the comments and now wondering if it has to do with the awkwardness of that bucket -- its name has a period in its name, so https validation fails and we had to workaround for that in datalad as well. In either case - having at least some debug log message about the problem would be handy

test@hopa:/tmp$ mkdir testuser
test@hopa:/tmp$ cd testuser
test@hopa:/tmp/testuser$ git clone https://github.com/OpenNeuroDatasets/ds001506 ; cd ds001506; 
Cloning into 'ds001506'...
remote: Counting objects: 11017, done.
remote: Compressing objects: 100% (6694/6694), done.
remote: Total 11017 (delta 1856), reused 11007 (delta 1846), pack-reused 0
Receiving objects: 100% (11017/11017), 1.17 MiB | 1.31 MiB/s, done.
Resolving deltas: 100% (1856/1856), done.
test@hopa:/tmp/testuser/ds001506$ git annex enableremote s3-PUBLIC public=yes
(merging origin/git-annex into git-annex...)
(recording state in git...)
download failed: ConnectionFailure Network.Socket.connect: <socket: 11>: timeout (Connection timed out)

  Remote origin not usable by git-annex; setting annex-ignore
enableremote s3-PUBLIC ok
(recording state in git...)
test@hopa:/tmp/testuser/ds001506$ git annex get --debug sub-01/ses-anatomy/anat
[2018-09-11 13:00:24.89648131] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","ls-files","--cached","-z","--","sub-01/ses-anatomy/anat"]
get sub-01/ses-anatomy/anat/sub-01_ses-anatomy_T1w.nii.gz [2018-09-11 13:00:24.900815381] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","show-ref","git-annex"]
[2018-09-11 13:00:24.90536002] process done ExitSuccess
[2018-09-11 13:00:24.905485937] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","show-ref","--hash","refs/heads/git-annex"]
[2018-09-11 13:00:24.909586624] process done ExitSuccess
[2018-09-11 13:00:24.909805571] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","log","refs/heads/git-annex..a152bc6cd4a6b1f06115d683e6a296374219e9f7","--pretty=%H","-n1"]
[2018-09-11 13:00:24.914170223] process done ExitSuccess
[2018-09-11 13:00:24.914585144] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","cat-file","--batch"]
[2018-09-11 13:00:24.91587481] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","cat-file","--batch-check=%(objectname) %(objecttype) %(objectsize)"]
(from s3-PUBLIC...) [2018-09-11 13:00:24.982444067] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","diff-tree","-z","--raw","--no-renames","-l0","-r","4b825dc642cb6eb9a060e54bf8d69288fbee4904","18df0d827a901db0a989999f765f2816b769bf49","--"]
[2018-09-11 13:00:24.994539395] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","cat-file","--batch"]
[2018-09-11 13:00:24.995000749] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","cat-file","--batch-check=%(objectname) %(objecttype) %(objectsize)"]
[2018-09-11 13:00:25.433359795] process done ExitSuccess

  Unable to access these remotes: s3-PUBLIC

  Try making some of these repositories available:
    810b2f6b-fb98-4401-9130-6c84dd7ddc50 -- root@b3ba225d5547:/datalad/ds001506
    ca9b233b-7567-48b3-89c7-efe7f6a97d4a -- [s3-PUBLIC]

  (Note that these git remotes have annex-ignore set: origin)
failed
[2018-09-11 13:00:25.657658586] process done ExitSuccess
[2018-09-11 13:00:25.658108866] process done ExitSuccess
[2018-09-11 13:00:25.658390098] process done ExitSuccess
[2018-09-11 13:00:25.658635699] process done ExitSuccess
git-annex: get: 1 failed
test@hopa:/tmp/testuser/ds001506$ git annex version | head -n 1
git-annex version: 6.20180807+git230-gaa291acfe-1~ndall+1
test@hopa:/tmp/testuser/ds001506$ git annex info s3-PUBLIC
uuid: ca9b233b-7567-48b3-89c7-efe7f6a97d4a
description: [s3-PUBLIC]
remote: s3-PUBLIC
trust: untrusted
cost: 200.0
type: S3
creds: not available
bucket: openneuro.org
endpoint: s3.amazonaws.com
port: 80
storage class: STANDARD
partsize: 1.07 gigabytes
public: yes
versioning: no
encryption: none
chunking: none
export: yes
remote annex keys: 1287
remote annex size: 103.28 gigabytes (+ 632 unknown size)

fixed as the one no longer observed --yarikoptic