Are you new to AE? Sure sounds like it!
You need to know that using AE is NOT intuitive -- you can't learn by doing. It's not the kind of application where you learn a couple-three tricks and you're good to go. You can't assume it works like an editing application, because it DOES NOT.
Do yourself a favor. Save your sanity. Begin at the beginning. Blow it off at your peril:
Now, this stuff may not solve all your woes. The most recent versions of AE are notorious for behaving screwy for a lot of people. You may actually have some weird, off-the-wall problem. But you won't know until you know a bit about running AE properly.
Welcome to the Brave New World that is Adobe. It ain't for the feint of heart.
If you're using 13.5, you're going to have problems. It had some huge issues. Adobe has sorted many of them out already. Update to 13.7.2 and things should be much better.
Also, if you're new to AE, keep in mind that AE is not a video editing program. A preview must be cached first before it can play back in real time.
I'm not a noob to After Effects Dave, i have been using it for the last 7 years. This problem is new. Probably since they rewrote most of it for CC. I think anyone would feel hard done by if you cannot RAM preview any of your stuff in realtime all of a sudden, how are you supposed to get anything done?
I have done my research, conclusion being that 13.5 is crappy. I was hoping perhaps there's a new setting i'm missing. Not to be directed to beginners tutorials.
I guess my answer has been answered since we all agree it's buggy.
Yup. Nobody is going to argue that 13.5 had issues. That's why you shouldn't use it. Use 13.7.2 on Mac 13.7.1 on PC and it actually works pretty well. Hopefully the next version that should be releasing this month or next (if past years are any indication) will be even better as their sneak peek videos seem to be mostly focused on stability and speed.