Check 2. Restart the devices
Try restarting your Galaxy phone, router, and modem.
Step 1.To restart your phone, tap the Power icon in the Quick panel, then tap Restart.
Step 2. Turn your router and modem off and on again. When turning the router and modem off, unplug the power plug and plug it back in, and then turn on the power.
Step 3. After you restart each device,see if you fixed the issue.