DIAGNOSIS The printer's IP address changed after your router rebooted. Your computer is looking for the old address.
FIX On the printer's OLED screen, press the Setup button. Navigate to Device settings > LAN settings > Confirm LAN settings. Note the current IP address. On your Windows PC, go to Control Panel > Devices and Printers. Right-click your TS6520, choose Printer Properties. Go to the Ports tab. Find and select the port with the matching IP address. If none match, add a new Standard TCP/IP Port using the new IP address.
IF THAT DIDN'T WORK Your firewall or antivirus is blocking the connection. Temporarily disable them and try to print a test page. If it works, add an exception for your printer's IP address in your security software.
HEADS UP Setting a static IP for the printer in your router settings prevents this. Do it from your router's admin page, not the printer.