Crashes to Desktop, or goes into a infinite loading loop in Steam Client.

[Bassblitzed]

KSP: 1.2.1 64-bit

Problem: Crashes to Desktop and or freezes indefinately

Mods Installed: KAS 0.5.9 (Upgraded to 0.6.0 and tested also) KIS 1.2.12 (Upgraded to 1.3.0 and tested) MiniAVC, ModuleManager 2.6.25 (Upgraded to 2.7.2, and 2.7.4 and tested) (Tested with clean install and NO mods installed, still crashes through Steam.)

Reproduction: Install KSP 1.2.1 on macOS Sierra Beta 2 and run through Steam. Game refuses to load and freezes/crashes to desktop about 25/75% of time. Never correctly launches.

Log files: https://drive.google.com/drive/folders/0B5pkscNB5-75NkFqRnMwTnBiY3M?usp=sharing

I have been playing KSP via Steam client for a couple months now, bought it back in September. Recently, I upgraded my OS to Sierra 10.12.2 Public Beta, and KSP ran fine still, but only for a while. I had several mods installed at the time, MechJeb2 (which was installed incorrectly, being one folder level too deep, and would not load any required packages), KIS 1.2.12, NearFutureSolar 0.6.2 (also installed incorrectly because I had not removed the contents from the internal gamedata folder), KAS 0.5.9, Kerbal Alarm Clock 3.7.1.0 (not installed correctly) , DockingPortAlignment 6.4 , and ModuleManager 2.6.25, and MiniAVC which was included with the packs. The reason I installed so many of these incorrectly is because I didn't know to remove the other folder sublevels (Shame on me for not reading the readme's) But since KIS and KAS seemed to work I didn't try to mess with it anymore. Since then I have correctly installed all my modpacks and have resolved the issue, because launching the game from the folder through the launcher without using the steam launcher seems to work completely fine, and I would imagine this is fairly similar to this issue. (Link1 Link2 Link3) But what is odd is that all my other Steam games run fine- and I have since updated all my mods to be 1.2 compatible, and once again it works fine, BUT only when I launch from outside steam. I tried running 1.2 without any mods, and deleting the entire folder and reinstalling from clean install, Didn't work through steam. I tried validating all the files, and checked out. If you have any idea what the issue is, please let me know. I would like to run KSP through steam again to log hours and get achievements. Thanks!

[Phineas Freak]

Steam probably installed KSP 1.2.1 on top of the previous installation. Remove all mods, clean the Steam KSP folder, reinstall KSP and reinstall your mods.

[DoctorDavinci]

Hope these help you with your CTD's .....