Hello @AL-MAMUN 

Thank you for reporting the issue to the community.

May I know the frequency of this issue? Who is your ISP? Is the line or the modem not stable?

When this issue occurs, don't reboot the router, just login to its web interface, then check the Internet status, if there is still showing the correct PPPoE connection, try to disconnect manually and reconnect on the page, check if the internet will be back.

Please also email the router system log to support.forum@tp-link.com for further analysis, be sure the system log includes the progress when the router loses the connection and then connects back when you click disconnect/reconnect on its page.