Keep up the good work Paul and JS team. I've been in the IT industry for 25 years now, and I've never seen a major version update of any software not have some issues, even after extensive beta testing. I remember arriving on site one day and nothing was working, a critical securty update from Ubuntu bricked specific Dell server models, unfortunately, the ones we had. It was a 2 minute job to roll back until Ubuntu released another kernel update.
It is very exciting to have new software, but sometimes it is best to sit back and wait. Read the support forums to see if there is a pattern of issues, and determine if these issues will affect your sites. Then and only then, after you've backed up your site, and tested that you can restore from the backup, deploy the updates. This is just standard practice for any software, not just web platforms.
I've deployed on 3 live sites now, and only 1 site had minor issues with the titles on 2 pages. I've only used custom.css to modify the Helix Ultimate template though, and I don't use any third party plugins apart from Akeeba Backup and JCE Pro. The site that had the minor issues was one of the first that I developed with Helix and Pagebuilder Pro, so it was possibly something I did wrong anyway.