I posted this a while back in the comments after build release .106. I have tried every other build since then, up to .121 and the new (to me) problem still exists...
A pro VST plugin I use, the IK Multimedia ARC System (latest version), works perfectly in other hosts (i.e. Cubase) but does not always load correctly in MC14 beyond .101. Specifically: intermittently its effect in the chain is not audible unless I open the DSP studio and actually display the plugin's interface - then I hear the effect kick in. Although it remains checked "on" and active, sometimes it does not affect the sound as it should unless I "look at it". Once displayed, the effect remains active throughout the MC14 session until application restart.
More importantly,
1) If I update MC14 from .101 to anything else (up to .121 tested), the next time I display the 'page' for that plugin in the DSP studio, its Licensing and Activation windows comes up as if I've never properly activated the plugin. Of course I have, long ago, in .101 or before.
2) When I display that 'page', the whole DSP studio windows contracts to a teeny-weeny window with just the window control buttons.
So in summary, I used this licensed, registered, pro VST plugin 100% perfectly in MC14 up to .101 and now every subsequent build blows it away. Am stuck in .101 'til this has a fix.