well I can't tell you what is going wrong. At some points I had trouble with iwd, but this is way back in the beginning of switching to iwd. In some cases it is better to use wpa. mostly enterprise setups and some exotic setups.
Also hidden networks can produce trouble, like my wifi setup, bit complex but it works and iwd connects automatically to it. In the beginning I had trouble but not yet anymore. What I do is always to setup my WiFi connection as root, when possible. Second I prefer to use the client-tools over the graphical to set it up. later for fast switching i use the GUI.
But if you use it on a headless system, use the cli-tools. its most more easy than all that blinky shiny gui thingy.