DIAGNOSIS This is typically a software glitch in the TV's network module or an incompatibility with certain router settings (like WPA3 or a 5GHz channel width).
FIX First, power cycle both your router and the TV. Unplug both for 2 minutes. Restart the router first, wait for it to be fully online, then plug the TV back in. On the TV, go to All Settings > Connection > Wi-Fi Connection and select 'Reconnect'. If it fails, choose 'Network Initialization' to clear all old network data, then try again.
IF THAT DIDN'T WORK Log into your router and temporarily change the Wi-Fi security from WPA3 to WPA2/WPA3 mixed mode. Also, try setting your 5GHz band to a channel below 100 and a channel width of 40MHz or 80MHz, not 160MHz. The TV's Wi-Fi chip can be finicky with advanced settings.
HEADS UP For consistent 4K streaming, a wired Ethernet connection is always better. The C3 has a 100Mbps Ethernet port, which is sufficient for most streams. If you need faster speeds (e.g., for large local file playback), use a USB 3.0 to Gigabit Ethernet adapter in the TV's USB port.