Currently we are doing content migration from AEM 6.2 to AEM 6.3. After migrating the content to AEM 6.3 Side Rail and Edit Bar is not getting displayed in the content.
And it showing some Js Error in the browser. Given the snap-shot of the same for your reference.
This is an upgrade bug - you may need a hotfix. I recommend opening a support ticket. There is not much the community can do when you are faced with broken software.