If the client refuses to open or closes immediately, start with the basics: clear the cache folder (on Windows it's %localappdata%\Roblox\logs), reinstall the desktop app, and make sure your graphics drivers are up to date. Integrated Intel GPUs older than 2014 often cause crashes — switching renderer to OpenGL in the settings can help.
Latency above 150ms usually points to your connection, not the servers. Run a quick test at fast.com and check if other devices on the same network are eating bandwidth. Wired connection beats Wi-Fi every time here. Also check if your firewall is throttling UDP traffic — Roblox uses ports 49152–65535.
Error code 403 on login typically means too many failed attempts triggered a temporary block. Wait 15–20 minutes, then try again. If you use a school or corporate network, the platform might be restricted at the router level — try mobile data to confirm.
Blank textures or missing items in the catalog almost always mean a partial cache corruption. Delete everything inside %localappdata%\Roblox\versions and let the client re-download. On mobile, a full reinstall is the fastest fix.
If messages disappear without delivery, the chat filter might be silently blocking them — this happens with new accounts under 13. Check your privacy settings under Account > Privacy and make sure 'Who can chat with me' isn't set to 'No one'. If settings look fine, the issue is likely a temporary server hiccup on their end.