This must be a simple check box I flubbed somewhere, but google and this forum's search has been less than forthcoming.
Typically when I pressed the spacebar in aftereffects it would play back from the point in time designated in the composition timeline and begin its slow march to the right only when it encounters unrendered sections in the timeline. Historically if I were to pause the preview it would being to play back the already rendered bits in realtime for my review.
Now, when I hit playback it doesn't play a single frame until it encounters a unrendered bit in the timeline, preventing me from reviewing already previewed parts of the timeline.
Machine is a 4790k / 32GB Ram / SSD main drive and scratch drive / Windows 8.1 and aftereffects 2015.3
The Preview panel offers more options than ever before. you should read through here: Preview without rendering in After Effects
the default spacebar is different from the old space bar, but you can change it to the old behavior. if I remember correctly, these are the settings that are the old Spacebar behavior:
Yep, this can happen... thank you for the feedback!