1) Run Pre-Upgrade steps2) Stop the 6.3 instance3) Replace the jar as migration is not required when moving from 6.3 to 6.54) Unpack the jar and start the 6.5 instance.More details at [1][1] Performing an In-Place Upgrade

Have you compiled the custom code with uber jar version 6.5.0.0 ?

Do you see any error in the "Developers Console" for Chrome? Also, check the "Network" tab under the same console for any failures.

Sling Mapping Or Redirects at apache level are the only options. In this case, authors have to assume that "/content/dam" will be replaced by "/" when the page/asset will be loaded on the publish instance Or live site.NOTE: Do not use sling mappings on author instance as it is only recommended to be...

Do you see anything in the SAML logs?You can set up a Logger in order to debug any issues that might arise from misconfiguring SAML. You can do this by:Going to the Web Console, at http://localhost:4502/system/console/configMgrSearch for and click on the entry called Apache Sling Logging Logger Conf...

Do you see the same issue on IE edge?

Can you share the final command you used for migration?

There were some multifield issues that were fixed in the latest CFP's. Can you try installing the latest SP/CFP and update the thread if you still see the same issue?

I believe you have to find the inheritance fucntionality under /libs and customize under /apps as per the business requirement.

Is this only happening for the Forum component? Can you try with another OOTB component?