R6120 - Chromecast can't access internet

For the last few days, I am unable to use chromecast with my router. I have been using this router for almost 1 year with chromecast working fine. I tried all the options like resetting chromecase, resetting router, resetting google home and reinstalling, but I keep getting stuck at "Chromecast 'XYZ' is connected to 'NAME' Wi-Fi Network, but can't access the internet". I moved my chromecast near my router but it made no difference. I finally took my chromecast to another place to connect to another router to check if chromecast has gone bad, but I was able to connect there. So, I came back home and tried to downgrade my firmware version step by step : V1.0.0.72,70,68,56; but still no success. I hope the developers of this device/software or people who have experience in this matter can shed some light.