Try to clean the web browser cache, and change to another browser like Firefox, then login.
Or try to reset the router, it shoud work.

TP-LINK support advised reset to factory defaults and check for fields populating. I tried the Factory Restore button in the Advanced Settings/System Tools/Backup & Restore page. The router login page never displayed. I then held the reset button on the back of router and after some time the login page displayed, the fields were populated and remained until later when a configuration change required a reboot. After that the fields were missing again. I have reported this to the support person and requested the firmware team to investigate. Will advise if there are more updates. I also discovered the status
page is a snapshot as the cpu and memory fields do not update unless the web page is refreshed. Flushing the browser cache did not help. I do not use cache on the browser any way, so it probably would not have helped for me. That is all for now.