Linux – Cannot connect to WiFi with nmcli, although secrets are provided

I am using nmcli on ArchLinux (version 1.14.5dev+17+gba83251bb-1 from the official package repository) to connect to wifi. This works perfectly for all wireless networks apart from this one Vodafone EasyBox network.

Trying to activate the connection with the correct password gives me the following error message:

Passwords or encryption keys are required to access the wireless network 'EasyBox-123456'.
Warning: password for '802-11-wireless-security.psk' not given in 'passwd-file' and nmcli cannot ask without '--ask' option.
Error: Connection activation failed: Secrets were required, but not provided

However, 802-11-wireless-security.psk is stored, as you can see here:

$ nmcli con show EasyBox-123456
connection.id:                          EasyBox-123456
connection.uuid:                        <hidden>
connection.stable-id:                   --
connection.type:                        802-11-wireless
connection.interface-name:              --
connection.autoconnect:                 yes
connection.autoconnect-priority:        0
connection.autoconnect-retries:         -1 (default)
connection.multi-connect:               0 (default)
connection.auth-retries:                -1
connection.timestamp:                   0
connection.read-only:                   no
connection.permissions:                 --
connection.zone:                        --
connection.master:                      --
connection.slave-type:                  --
connection.autoconnect-slaves:          -1 (default)
connection.secondaries:                 --
connection.gateway-ping-timeout:        0
connection.metered:                     unknown
connection.lldp:                        default
connection.mdns:                        -1 (default)
connection.llmnr:                       -1 (default)
802-11-wireless.ssid:                   EasyBox-123456
802-11-wireless.mode:                   infrastructure
802-11-wireless.band:                   --
802-11-wireless.channel:                0
802-11-wireless.bssid:                  --
802-11-wireless.rate:                   0
802-11-wireless.tx-power:               0
802-11-wireless.mac-address:            <hidden>
802-11-wireless.cloned-mac-address:     --
802-11-wireless.generate-mac-address-mask:--
802-11-wireless.mac-address-blacklist:  --
802-11-wireless.mac-address-randomization:default
802-11-wireless.mtu:                    auto
802-11-wireless.seen-bssids:            --
802-11-wireless.hidden:                 no
802-11-wireless.powersave:              0 (default)
802-11-wireless.wake-on-wlan:           0x1 (default)
802-11-wireless-security.key-mgmt:      wpa-psk
802-11-wireless-security.wep-tx-keyidx: 0
802-11-wireless-security.auth-alg:      open
802-11-wireless-security.proto:         --
802-11-wireless-security.pairwise:      --
802-11-wireless-security.group:         --
802-11-wireless-security.pmf:           1 (disable)
802-11-wireless-security.leap-username: --
802-11-wireless-security.wep-key0:      <hidden>
802-11-wireless-security.wep-key1:      <hidden>
802-11-wireless-security.wep-key2:      <hidden>
802-11-wireless-security.wep-key3:      <hidden>
802-11-wireless-security.wep-key-flags: 0 (none)
802-11-wireless-security.wep-key-type:  unknown
802-11-wireless-security.psk:           <hidden>
802-11-wireless-security.psk-flags:     0 (none)
802-11-wireless-security.leap-password: <hidden>
802-11-wireless-security.leap-password-flags:0 (none)
802-11-wireless-security.wps-method:    0 (default)
802-11-wireless-security.fils:          0 (default)
ipv4.method:                            auto
ipv4.dns:                               --
ipv4.dns-search:                        --
ipv4.dns-options:                       ""
ipv4.dns-priority:                      0
ipv4.addresses:                         --
ipv4.gateway:                           --
ipv4.routes:                            --
ipv4.route-metric:                      -1
ipv4.route-table:                       0 (unspec)
ipv4.ignore-auto-routes:                no
ipv4.ignore-auto-dns:                   no
ipv4.dhcp-client-id:                    --
ipv4.dhcp-timeout:                      0 (default)
ipv4.dhcp-send-hostname:                yes
ipv4.dhcp-hostname:                     --
ipv4.dhcp-fqdn:                         --
ipv4.never-default:                     no
ipv4.may-fail:                          yes
ipv4.dad-timeout:                       -1 (default)
ipv6.method:                            auto
ipv6.dns:                               --
ipv6.dns-search:                        --
ipv6.dns-options:                       ""
ipv6.dns-priority:                      0
ipv6.addresses:                         --
ipv6.gateway:                           --
ipv6.routes:                            --
ipv6.route-metric:                      -1
ipv6.route-table:                       0 (unspec)
ipv6.ignore-auto-routes:                no
ipv6.ignore-auto-dns:                   no
ipv6.never-default:                     no
ipv6.may-fail:                          yes
ipv6.ip6-privacy:                       -1 (unknown)
ipv6.addr-gen-mode:                     stable-privacy
ipv6.dhcp-duid:                         --
ipv6.dhcp-send-hostname:                yes
ipv6.dhcp-hostname:                     --
ipv6.token:                             --
proxy.method:                           none
proxy.browser-only:                     no
proxy.pac-url:                          --
proxy.pac-script:                       --

I tried several things, including restart NetworkManager/wpa-supplicant, the router, and disabling PMF, but nothing worked.

Specifying --ask asks me for a password, but gives me the same error message afterwards. Removing and recreating the connection using nm-connection-editor didn't work either. It works without any problems on my Android device.

How can I connect to this Network?