DIAGNOSIS This is almost always a Wi-Fi setup issue. The dishwasher's wireless module is finicky and needs a 2.4 GHz network signal (not 5GHz) and a strong signal from your router.
FIX First, reset the dishwasher's network. Press and hold the Wi-Fi button on the control panel for 3 seconds until it beeps. Then, in the LG SmartThinQ app, delete the dishwasher and start the "add device" process from scratch. Make sure your phone is connected to your 2.4 GHz Wi-Fi band during setup.
IF THAT DIDN'T WORK Your router might be using a setting that the dishwasher doesn't like, like WPA3 security or a hidden SSID. Temporarily switch your 2.4 GHz band to WPA2 security and make sure the SSID is broadcast. Try the setup again.
HEADS UP The dishwasher's Wi-Fi antenna isn't super powerful. If your router is far away or through several walls, the connection will be flaky even if it initially pairs. A weak signal will cause it to drop off the network constantly.