@viveksachdeva [EDIT] -- revising my post to reduce confusion -- the fix is within build --> com.adobe.granite.crx-packagemgr-1.2.100.jar    

May want to log a ticket. DISP-818 removed the Cache-Control header from requests with query parameters BUT -- this introduced some unintended things which are currently being handled under the open JIRA GRANITE-29891  

This issue has been observed by quite a few people and organizations.Specific to build 83.0.4103.61 of Google Chrome.

You should probably move away from ExtJS use in AEM. It's been in a deprecated state for several years / major releases.

What does metadata have to do with anything here? Restrict the folder by MIME type.

Sure, authentication handlers register on paths you define, so you should be okay here. P.S. Time to upgrade off 6.1

RE : i bought up the new slave instance and incremental index started running for a so long time. <-- what do you mean exactly?

There are absolutely zero elements of Flash within AEM.Any Flash content was removed from the product back in AEM 6.3.

Of course. See : https://docs.adobe.com/content/help/en/experience-manager-65/assets/administer/metadata-schemas.html#apply-folder-specific-metadata  

The Wknd Tutorial is a good step by step guide. Start here : https://docs.adobe.com/content/help/en/experience-manager-learn/getting-started-wknd-tutorial-develop/overview.html