Upgrading fails after downgrading the router R8000P firmware

Hi I have R8000P router .

An error occurred that a specific web page could not be connected while using a router.

As a result of a community search, there is a DNS server issue, and downgrading the firmware will solve it.

So I downgraded the firmware (Firmware Version v1.3.0.10_1.2.2 )
After that, the internet connection was often persistent.

Can't upgrade back to the latest version.
It automatically reboots after uploading the latest version, but the firmware is still the old version.

The current status of the router.

I did Manual update, TFTP update but not working. 

Please let me know , how to solve it ?