Comment # 1 on bug 1047857 from Markus Greger

Workaround:

Manually setting MAC address outside of NetworkManager like the following
command sequence (just replace $MacAddrAsInNetworkMgrConnection with wanted
MAC) will enable NetworkManger to successfully connect using a connection with
cloned mac address set to $MacAddrAsInNetworkMgrConnection.

nmcli r wifi off; 
ifconfig wlan0 hw ether $MacAddrAsInNetworkMgrConnection; 
nmcli r wifi on


It likely only works once, as NetworkManager past version 0.8.2 may reset it
later as https://bugzilla.gnome.org/show_bug.cgi?id=770611#c4 states.