Swipl hangs on "http_post/4"

On my mac, I am using the latest development version of swi

Welcome to SWI-Prolog (threaded, 64 bits, version 9.1.7)

When running the following query, it seems that it spends an awful lot of time on a call to http_post/4.
By comparison, the same routine returns immediately and successfully when using the latest stable release.
Is there something that changed between the 2 versions?

The context of the call is:

make_session(Token) :-
	retractall(session_info(_, _, _))
	, setting(api_login_url, Url)
	, setting(api_login, Login)
	, setting(api_password, Passwd)
	, atom_json_dict(A, _{login_email: Login, login_password: Passwd}, [])
	, http_post(Url, atom('application/json', A), Data, [])
	, atom_json_dict(Data, _{ token:Token}, [value_string_as(atom)])
        , ......