I am unable to reproduce the JSON error, however I can reproduce a problem where the command returns immediately without downloading any files. Note that with this specific directory there are 4300+ files and the first thing that happens in a wildcard 'get' command is that the directory listing is expanded, for a large directory this can take a while before the downloads begin -- are you sure this isn't what you were seeing? Adding a "verbose=True" option will have the task print out each file as it's processed and waiting a minute or two should be all that's needed before you see the downloads begin.
OTOH, if the command returns almost immediately without doing anything, it may indicate that there's a problem in your login tokens. Specifically, that the $HOME/.datalab/dl.conf file specifies one token saying you are logged in, but the $HOME/.datalab/id_token.derrcarr file contains a different token or doesn't exist. The fix here is to do a "datalab logout" to logout, remove the files in your $HOME/.datalab directory, and then a "datalab login" to login again. Using your token I was able to download ~2200 files before the disk filled up.
Hope this helps, please let us know if you continue to have problems.