Here is what I read:
Well put it this way i found out the hard way!
I upgraded to Sierra from El Capitan when i started Logic Pro 9 & went to the pull down menu to open & navigate to a Logic Pro 9 project it just kept crashing the only way i could open a project was to actually double click on the project file itself but then i could not save my project again crashing, so i decided to try to figure out the problem thinking maybe i need a clean install of Sierra.
So i did a clean install on another hard drive to test, my aim is just to get Logic Pro 9 installed nothing else keeping it all clean as possible i did not even sign in during install the cleaner the better, then Logic Pro 9 worked like normal & the most amazing thing is its running like it did in Snow Leopard no more graphics glitches when scrolling through EQ plugin the GUI/Graphics feels powerful, fast & solid again i am loving Sierra now.
I then signed into iCloud & started Logic Pro 9 the crash came back again exactly the same crash so i signed out then Logic Pro 9 worked like normal again, i then stayed signed & just disabled iCloud drive Logic Pro 9 still works like normal so i went back to my main Sierra from El Capitan hard drive disabled iCloud drive now i have Logic Pro 9 working & back to normal.
Also I recommend using Logic Pro 9.1.7 not Pro 9.1.8
Would be nice if Apple fixes this bug!