Ram preview plays back slow on 4k monitor unless I hide timeline panel
When your timeline panel is displayed on a large monitor, ram previewing is seriously compromised. If I simply hide the timeline, ram previewing works perfectly. I'm guessing that the code behind the timeline is super old, and needs to be free programs for bigger monitors.
8
votes

The latest (November 2019) release of After Effects includes major improvements to our preview architecture. You should see reliable, real-time playback of cached frames.
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Stéphane Augé commented
Same issue here. It is a bug related with 4k monitors. It appeared with CC 2015, CC 2014 is working perfectly smooth with 4k monitors.