[perh]

I know that I upgraded pretty fast. But that was due to getting close conectivity with iOS. And besides that I had NO problems with any other apps or plug-ins that I use with Logic Pro X.

Only AVID is causing problems.
I think it's not too much to ask these days to expect compatibility with the latest OS, as Apple run beta programs months before release. Even longer when it comes to close developer partners.
I don't buy into that it's because there is OS upgrades once a year, though I know it's frustrating for developers. AVID has ALWAYS been months behind in this game.
The reason is that they dont give a d.mn!
They are the industry standard, so they know we all depend on them!
That's the very simple psychological rason behind this.

But there really is NO excuse, as everybody does it better.
In most cases a lot of developers simply writes better code, and seems more focused to stick to Apple's guidelines for staying on edge with system changes. Often these changes are warned years before they are introduced or phased out.
Once in a while it is acceptable that it goes wrong. But not repeatedly! And I guess it will take months before it's fixed. And that is solely due to low priority. If it gets fixed at all. You never know.