I have 3.10.8, and I hit the same problem mentioned somewhere in the forum.
/usr/lib/lua/luci/cbi/datatypes.lua
doesnt contain base64 type etc. (https://github.com/openwrt/luci/commit/94d6b7b70d858c33ec0feabd22733c05c9fb529f).
I can see created peers in luci, but I cant create new (button) through the Luci.
root@Doma:~# opkg list | grep wiregu
kmod-wireguard - 4.4.161+0.0.20180918-1-0a333a8e606ab056173befac424900d2-1
luci-app-wireguard - git-18.145.30016-526a876-1
luci-proto-wireguard - git-18.145.30016-526a876-1
wireguard - 0.0.20180918-1
wireguard-tools - 0.0.20180918-1
LuCI 526a8767846acbe57c521912b35feb4d97354db6 branch (git-18.145.30016-526a876) / OpenWrt omnia 15.05 r47055