Diagnosis
This is almost always a router issue, not a dehumidifier problem. The unit's wifi module is basic and can get bumped off by signal interference or a router that's aggressively managing devices.
How to Fix It
Step 1: On your phone, forget the network your dehumidifier creates during setup (usually something like LG_Dehumidifier_XXXX). Step 2: Unplug the dehumidifier for 30 seconds. Step 3: While it's off, reboot your home router. Step 4: Plug the dehumidifier back in and go through the ThinQ app setup process fresh, making sure you're on a 2.4GHz wifi band (it doesn't support 5GHz).
If That Didn't Work
The dehumidifier might be too far from your router or in a signal dead zone. Try moving it temporarily closer to the router just for the initial setup and first few days of connection to solidify the link.
Heads Up
If you change your wifi password or get a new router, you will have to reset the dehumidifier's network connection from scratch using the button on the control panel or within the ThinQ app.