MyBB Community Forums

After making and successfully saving some changes in Css stylesheet, these changes do not reflect on forum instantly or after waiting for some time. They remain as it is and even inspect element field shows the old values. 
Did a hard refresh Ctrl +f5,  rebuild and reloaded cache several times, assigned CHMod 777 to all cache sub folders etc. but the issue remains. I am using chromium edge browser, tried another browser( chrome) but no luck regarding the above issue even tried clearing browser cache but issue remains.
Any help on this would be greatly appreciated.

Are you using Cloudflare ? If yes, clean its cache.
And if your server is nginx, you may have a css cache, peharps a force-reload may clean it

Do you use CloudFlare? If so, you will need to purge your cache there. Otherwise, you can contact your host and ask them to disable caching features on your forum.

Development mode is your best friend if using cloudflare and making changes to style sheets. Instead of putting cache every time you make a change it'll just turn it off up to 4 hours.