@paul you are saying: "Why do you have to upgarde to SPPB 4 right now? Cannot you wait for more fixed version."
Reason people are upgrading to the new version is JoomShaper's own blog: https://www.joomshaper.com/blog/sp-page-builder-v3-8-8
There you are promoting the upgrade to the new PageBuilder.
If migration is not advised, either take the blog offline or make a new blog where you telling that it is not wise to upgrade to the new SPB4.
Clear communication to end-users is the key in this part. On this moment SPB4 will cause a bad name to JoomShaper bij a lot of developers. Some will step away and think what the hell is going on with the quality Joomshaper had before.
Sometimes it's better to take a step slow then push thing in a rush. I am confident that Joomshaper will solve the issues in the future. For now I will stick to the PB3.