I had this exact problem...http doesnt work in release mode. In the end, it was because my SSL wasnt setup right. Try viewing your api in a normal chrome window (on android) and check if you get a green or red padlock.
For me, it was because I had forgot to concatenate my intermediate rapidSSL CA certificate to the certificate file pointed to by nginx.
Crosswalk shouldnt change its request behaviour between dev and release really...this wasted hours.