Hi everyone. I know this was an issue a while ago ... but just lately I'm having the same issue of not being able to top my previews.
The only way I can is to click on another comp tab then it stops.... or by hitting the spacebar a number of times!!! Sometimes like 10 times!
This is incredibly annoying and slows productivity unbelievably, as its very hard to change keyframes/edit etc while it's previewing.
It happens on all my recent projects... even on a simple one layered comp... this issue occurs.
MacPro6,1 12 core 64 GB RAM
After Effects CC 2015.3 Version: 126.96.36.199
HELP... VERY FRUSTRATING !
That sounds very frustrating. I don't have Yosemite to test on anymore, but things are working well on my MacBook with El Capitan.
Do you have another keyboard to test with on the off chance that something is awry with the spacebar?
The bug fix update to the CC 2017 release (After Effects version 14.0.1) fixes some issues that sound similar to this. You should give it a try, if you haven't already.