I can see the SSID, my router uses the correct encryption type, I have a reasonably long WiFi password, I can connect to a hotspot and via Ethernet but I still see the "Unable to connect" error when connecting to my WiFi network
a) A very rare issue can be the cause of this - the device can use the same subnet as your router (they would have the same IP address). If this is the case, the two devices will overlap and this will cause the device to behave erratically - randomly disconnecting etc.
This only happens if your router's IP address is 192.168.3.1 (this is the default Lattice IP address) - the ideal solution here is to change either the IP address of the Lattice1 or the router. I'll show you how to change the IP address of the Lattice.
First, you'll have to make sure you can connect to the device - since we're troubleshooting WiFi, your best bet here is connecting via Ethernet. Once your device is on your network, you will then SSH into your device and use the following commands:
uci set network.wlan.ipaddr=192.168.9.1
The new IP address from the first line can be whatever you want as long as it's unique within your network - we have used 192.168.9.1 as a general placeholder, but it's of course usable. Please note that if you ever reset the device's router, you will have to change the IP address manually again!
b) If changing your device IP address still doesn't resolve this issue, we would recommend you contact a networking expert at this point. The different configuration possibilities are almost endless and can be different with every router manufacturer and model.