I was going to post this to a new thread, but I seem to be having a similar problem.
I'm working in an entirely 2d comp (3894x720), doing some very simple text animation, and scaling/repositioning 1920x1080 video, totalling about 200 layers.
I just started having this problem, AE was working fine last night, but now all of my navigation within AE is very sluggish. Timeline marker takes anywhere from 2 to 6 seconds to appear where I click it, menus take just as long to pop up when I right click on a layer, even the cursor takes that long just to switch from regular black arrow to any other icon (for example when trying to extend a layer by dragging).
I have Fast Draft turned on for previews since I'm working in a 3-wide 1280x720 comp on an older machine. Video previews don't seem to be effected, it's just navigation.
I tried pre-comping as much as I could, but this had no effect. I also have the latest CC desktop and AE updates. A machine reboot had no effect.
I ran the activity monitor and found that when this was happening, my CPU usage for AE spiked up as high as 200% and never settled under 80%.
iMac late 2009
Processor 2.66 GHz Intel Core i5
Memory 16 GB 1067 MHz DDR3
Graphics ATI Radeon HD 4850 512 MB
Software OS X 10.9.1 (13B42)
Running AE CC
> Video previews don't seem to be effected, it's just navigation.
Try turning off Show Cache Indicators in the Timeline panel menu.
If my hunch is correct, the thing that is making navigation slow is the calculation to determine whether or not each frame in the cache is still valid, which can be very slow for compositions with expressions and certain time-based features. (BTW, I'm testing a fix for this right now, which we hope to make available in a release this spring.)
That seems to have fixed it. And I forgot to mention I'm using a throw expression to move some of my text.
That's the second quick, accurate reply I've gotten from you in two weeks. Hope you get paid adequately to put all the fires out over there.
Glad that I could help.