Kind of a late response, but maybe someone stumbles upon this same problem and may be looking for a solution.
EDIT: Looks like I was wrong with both solutions, since I happened to get exact same error. However I found a solution to this - simply set all
802-1x settings in one line, e.g.:
nmcli c modify <connection_name> 802-1x.eap <eap_mode> 802-1x.identity <username> 802-1x.phase2-auth <auth_type>
For what I've tested, these 3 settings are a minimum to setting
802-1x property. I will leave the previous answer, for I believe these still might be applicable as part of the solution.
Previous Solution (for reference)
This looks like you are trying to set
wifi-sec.key-mgmt connection property before setting
802.1x values. To put it simplier, you must put your edits in specified order, with
802.1x settings first, and
wifi-sec keys later.
However, if that is not the case - do you have your connection already added? You can add an empty template using following command:
nmcli con add type wifi [ifname <interface_name>] [con-name <connection_name_shown>] [ssid <ssid_of_wifi_connection>]
All parts (not sure about
 can be skipped, but you would need to add them through
modify command later on for the network to run, unless you only have 1 WLAN interface.