If the client freezes on startup or closes immediately, try deleting the lockfile in the installation folder — it's usually left over from a crashed session. If that doesn't help, run the client as administrator and check whether your antivirus is blocking any LoL processes. Riot Client sometimes conflicts with third-party overlays like Discord or GeForce Experience, so disabling them temporarily is worth a shot.
High latency is rarely a server issue — most of the time it's something on your end. Switch from Wi-Fi to a wired connection first. Then close any background apps that eat bandwidth: torrents, cloud sync, streaming. If ping stays high, run a traceroute to the game server to find out where packets are being dropped. Changing your DNS to 8.8.8.8 or 1.1.1.1 can also shave off a few milliseconds.
If an update hangs at a specific percentage, the issue is usually a corrupted download chunk. Open the Riot Client settings and run the built-in repair tool. If repair doesn't fix it, manually delete the contents of the 'Downloads' folder inside the game directory and restart the client — it'll re-fetch only what's missing. Make sure your firewall allows outbound connections on ports 443 and 2099.
Sudden freezes mid-match often point to overheating or driver issues rather than the game itself. Check GPU temperature with a tool like HWMonitor. Update your graphics drivers, and in the video settings switch from fullscreen to borderless window — this reduces the chance of the game losing focus and stuttering. Lowering shadow quality has a disproportionate impact on performance compared to other settings.
If the social panel stays empty or messages won't send, the XMPP service may be having trouble connecting. Restart the client completely rather than just closing the window — use Task Manager to kill all Riot-related processes first. If the problem persists, check that your system clock is set correctly, since certificate validation errors can silently break chat connectivity.