Since you have a gateway (modem plus router) it is harder to isolate possible ISP issues. Are you having issues with just WIFI or both WIFI and Ethernet connected devices? If your modem/router has logs, review them for any issues at the time of the failure. You need to check all of your ISP connections. If you have TVs or other devices such as phones connected to the ISP, those devices or the connectors and and splitters can cause issues so undo and redo all the connectors as some may be corroded. Be sure your firmware is up to date and you are using the power adapter that came with the modem/router. Also try disconnecting all of the Ethernet devices, power cycle the modem/router and test. Also this is a US based forum and you may get better results with the English forum which covers other countries outside the US. See https://community.tp-link.com/en/login (note the "en" vs the "us" in the link.