I'm having this issue as well, though it started in the past 6 months or so for me. Preview gets stuck and requires many presses of the spacebar to get it to stop looping. It does eventually stop, but it's super frustrating to have to press so many times, and it's so unreliable how many times are required. Sometimes 2, sometimes 7. Then sometimes you miss it and it starts previewing again and you're back at square one. Infuriating to say the least.

AE 23.3.0 (Build 107)

still a HUGE problem. This is a workflow killer. This should be such a high priority - something that has been broken for well over a year? I don't even understand how to get meaningful support at this point. Every time I talk to adobe support they just basically tell me to uninstall everything and start from scratch and not use any 3rd party plugins. How is that helpful? I can't wipe my machine clean all the time in the middle of projects and there's no professional out there that doesn't use 3rd party plugins. It's comical how slow AE interface runs on my 2017 imac pro with maxxed out specs (128gb ram, 18 core, radeon pro vega 64 16gb). This machine cost $12000 a few years ago - it's not a dinosaur, but AE runs like I'm trying to force the last bit of juice out of my 1998 imac G3.

This issue continues like so many others...

I'm also having this issue. Version 22.0.0, build 111. It's been going on for a while, though...

yeaah I experienced this problem too .. if the timeline reach the end of composition it looping and cant be stop

Spacebar preview looping never end !
Adobe never want to fix it.

I've read through many threads reporting this same problem. Essentially as soon as I start a preview, it will loop forever without end. No way to stop it. It also brings the entire computer to a crawl. This happens even if all I do is create a shape layer and do nothing to it. Previewing that alone loops. Only way to stop it is to kill the program.

I'm on a mac using the latest version of Catalina.
AE is version 18.0.0.

Happy to share anything else needed.

Hey Adobe, if you are listening, can you please fix this rampant software bug?

@Joseph Terrasi: Do you at least have them set to AutoSave every 20 minutes or so? You shouldn't be losing hours and hours. (well, I guess if that's cumulative, I can understand that)

And if another forum user starts with "you must be new to AE...." or the like, please just leave. If you use Premiere or AE and DON'T experience scores of bugs and crashes, you're the one who's new......

I have lost HOURS AND HOURS to this bug that Adobe has been saying it fixed since 2016 though it still arises in every version. AE and Premiere are the most expensive beta software in history, and this company will only spend money on new (also broken) programs.....

Same problem, updating to v17.7 doesn't solve. Happens across multiple projects, resolutions, etc. I have to force close the application every time I accidentally drag footage into the project window while RAM previewing.

Windows 10 Pro, i7-5960x, RTX 3090, 32GB RAM, SSD

I'll even take a preference option: Pause Preview when importing new files, as it always crashes when importing an item if the preview is already running.
I have to restart every time.
Incredibly annoying.

Windows 10, Ryzen 7 3800x, RTX 2070 super, 32GB RAM, SSD

Similar issue. 17.5.1 (but has been going on for months now) Windows 10, RTX 2060, 32GB RAM, 400GB external T7 SSD for cache

Seems to be consistent that if you preview, then don't edit anything but preview again, then it seems to go into this unresponsive state where it will build the preview in RAM (green line gets filled in if it isn't already) but then AE refuses to play back the preview until you close/restart AE (and AE usually goes completely unresponsive at this point too)

same issue:
iMac (Retina 5K, 27-inch, 2020)
8 GB 2667 MHz DDR4
Macintosh HD
AMD Radeon Pro 5300 4 GB

Same issue:
MacBook Pro 15" Retina Mid-2015, macOS Catalina 10.15.7
2.2 GHz Quad-Core i7
16 GB RAM
Graphics: Intel Iris Pro 1536 MB

AE: 17.5.0 (build 40)

Same issue:
MacBook Pro 15" Retina Mid-2015, macOS Catalina 10.15.7
2.2 GHz Quad-Core i7
16 GB RAM
Graphics: Intel Iris Pro 1536 MB

AE: 17.5.0 (build 40)

Same issue. Especially on short sequence lengths I can't get it to respond/stop without force closing. I've restored all the way back to 17.0.5 and it still happens. I've even downgraded drivers with the same issue.

Especially an issue with 32bpc.

AE 17.0.5 and later (i believe all later but haven't tried all)

WIn 10 64
i7 5930K
32gb ram
GPU 980TI
Also happens with 2x980TI + 1x 980

Doesn't happen on my Razer 2019 Laptop w 2080

This is happening to me as well and I have a theory on what's causing it - if you are working in full resolution on a 4k project, and the comp viewer scale is at 25%, the comp viewer falls behind struggling to downscale each frame from RAM.

The info panel can say it's playing at real-time, but it actually isn't due to the extra time spent downscaling and I think this causes a desync. So let's say RAM is running real-time and you press space while it's at frame 50, but the comp view hasn't even gotten to frame 30 yet: the input gets delayed until the comp view catches up to frame 50.

This delay grows the longer you let the preview run, and gets worse the smaller the comp viewer scale is. So the delay until your input is finally recognized could be seconds to minutes long depending.

The workaround is to lower the preview resolution or only preview at 100% scale

Yep, same thing. I'm just doing the first tutorial and I'm getting this problem.

Mac Mini Late 2014
3 GHz Intel Core i7
16 GB 1600 MHz DDR3
Intel Iris 1536 MB graphics

Using macOS Mojave 10.14.5,

After Effects 17.1.4