Thank you ande for this simple solution! It definitely worked for me on my TL-ER6020. I disabled all dynamic dns services and now it seems to work fine. I also used the no-ip service. :o

I have the same problem with the TL-ER6020 since upgrade to the newest firmware 150416. The router seems to work fine but the webinterface gets messed up after an uptime of some days. Only a manual...