I had a problem with the wifi after upgrading it to 4.1 unstable. My ethernet was working nicely, only wifi had problem.
On recalbox.config do you see your wifi name and password correctly? OK That's your SHARE folder right?
Now do the same on the SHARE_INIT folder, recalbox.conf file, wifi name and password probably is empty, soo fill it up.
Mine worked correctly after this.
Hope it works for you =D