Diagnosis
This is a known quirk with some Hisense TVs and certain router setups, often related to power-saving features or IP address conflicts.
How to Fix It
First, give your TV a static IP address on your network. On the TV, go to Settings > Network > Your Network > Advanced. Change 'IP Settings' from DHCP to Static. Enter an IP address that's outside your router's DHCP range (e.g., if your router gives out addresses like 192.168.1.100-150, use 192.168.1.99). Fill in the gateway and DNS (usually your router's IP, like 192.168.1.1). This stops the router from potentially bumping the TV off.
If That Didn't Work
The TV's WiFi power-saving can be too aggressive. In the same Network settings, look for a 'WiFi Power Saving' or 'WiFi Sleep Policy' option and turn it OFF. Also, if you have a dual-band router (2.4GHz and 5GHz), try connecting the TV to the 2.4GHz network only. It has longer range and is often more stable for smart home devices, even if it's slower.
Heads Up
If you've recently changed your WiFi password, the TV might be trying an old saved network. Go to Settings > Network > Your Network and select 'Forget'. Then reconnect fresh. Also, a cheap Ethernet-to-USB adapter can give you a rock-solid wired connection if your router is nearby.