Please describe the problem.

original report: https://github.com/datalad/datalad/issues/3583

What steps will reproduce the problem?

initial get -J8 largely fails (ok for 1 file in one thread I guess) but subsequent succeeds:

hopa:/tmp
$> git clone https://github.com/OpenNeuroDatasets/ds000248 && cd ds000248 && git annex init && git annex get -J 8 sub-01 
Cloning into 'ds000248'...                                                                                     
remote: Enumerating objects: 161, done.
remote: Total 161 (delta 0), reused 0 (delta 0), pack-reused 161
Receiving objects: 100% (161/161), 18.55 KiB | 863.00 KiB/s, done.
Resolving deltas: 100% (20/20), done.
CHANGES  acq-epi_T1w.json  acq-flipangle05_run-01_MEFLASH.json  acq-flipangle30_run-01_MEFLASH.json  dataset_description.json  derivatives/  sub-01/  sub-emptyroom/
init  (merging origin/git-annex into git-annex...)
(recording state in git...)

  Remote origin not usable by git-annex; setting annex-ignore
(Auto enabling special remote s3-PUBLIC...)
ok
(recording state in git...)
get sub-01/meg/sub-01_task-audiovisual_run-01_meg.fif (from s3-PUBLIC...) 
  Remote is configured to use versioning, but no S3 version ID is recorded for this key

  unknown export location

  Unable to access these remotes: s3-PUBLIC

  Try making some of these repositories available:
    82a4b182-753f-4d93-a59e-20cfdd4d4237 -- [s3-PUBLIC]
    e3612a8a-0c48-4374-9bfb-888f4010be54 -- root@1f69c4ed80cf:/datalad/ds000248

  (Note that these git remotes have annex-ignore set: origin)
failed
get sub-01/anat/sub-01_acq-flipangle30_run-01_MEFLASH.nii.gz (from s3-PUBLIC...) 
  Remote is configured to use versioning, but no S3 version ID is recorded for this key

  unknown export location

  Unable to access these remotes: s3-PUBLIC

  Try making some of these repositories available:
    82a4b182-753f-4d93-a59e-20cfdd4d4237 -- [s3-PUBLIC]
    e3612a8a-0c48-4374-9bfb-888f4010be54 -- root@1f69c4ed80cf:/datalad/ds000248

  (Note that these git remotes have annex-ignore set: origin)
failed
get sub-01/anat/sub-01_T1w.nii.gz (from s3-PUBLIC...) 
  Remote is configured to use versioning, but no S3 version ID is recorded for this key

  unknown export location

  Unable to access these remotes: s3-PUBLIC

  Try making some of these repositories available:
    82a4b182-753f-4d93-a59e-20cfdd4d4237 -- [s3-PUBLIC]
    e3612a8a-0c48-4374-9bfb-888f4010be54 -- root@1f69c4ed80cf:/datalad/ds000248

  (Note that these git remotes have annex-ignore set: origin)
failed
get sub-01/anat/sub-01_acq-flipangle05_run-01_MEFLASH.nii.gz (from s3-PUBLIC...) 
  Remote is configured to use versioning, but no S3 version ID is recorded for this key
(checksum...) ok
(recording state in git...)
git-annex: get: 3 failed

$> git annex get -J 8 sub-01
get sub-01/anat/sub-01_T1w.nii.gz (from s3-PUBLIC...) 
  Remote is configured to use versioning, but no S3 version ID is recorded for this key
(checksum...) ok
get sub-01/anat/sub-01_acq-flipangle30_run-01_MEFLASH.nii.gz (from s3-PUBLIC...) 
  Remote is configured to use versioning, but no S3 version ID is recorded for this key
(checksum...) ok
get sub-01/meg/sub-01_task-audiovisual_run-01_meg.fif (from s3-PUBLIC...) 
  Remote is configured to use versioning, but no S3 version ID is recorded for this key
(checksum...) ok
(recording state in git...)

What version of git-annex are you using? On what operating system?

7.20190708+git36-g32d526164-1~ndall+1