Yep, same issue.

iMac 5k, 27-inch
Processor: 4 GHz Quad-Core Intell Core i7
Memory: 32 GB 1867 MHz DDR3
Graphics: AMD Radeon R9 M395X 4 GB

Using AE 17.1.4

If I'm editing a large 4k comp it freezes and is unresponsive and keeps looping. Sometimes I can press spacebar or click the timeline to pause it but most of the time I have to close the app.

I can't preview my work so this makes AE useless.

Fix please Adobe!!!!!!!!!!

Programme becomes laggy and a lot of the time unresponsive during playback. I can start playback on a section and then it won't stop (clicking the playhead, clicking button in Preview menu or hitting Space)

After Effects CC 2020 17.1.4 (Build 37)
Macbook Pro 15" 2016
Processor 2.9GHz Quad-Core Intel Core i77
Memory 16GB
Graphics Radeon Pro 460 4GB - Intel HD Graphics 530 1536MB

Same here. macOS Catalina, Adobe 2020, can't stop RAM preview without force close. Making After Effects completely unusable. Have to go back to 2019 until this is addressed.

One tip that might help is that when I switch to different application, that'll stop to ram preview in most cases. So command+tab on a mac will at least break this cycle of madness for me.

Same problem. Even on a short RAM preview (57 frames) I can rarely break the looping animation. Occasionally it will respond, but it may take more than a minute to do so after I hit the stop button (and if I get impatient and hit it again, if it responds at all, it will do a double click and start all over again). I often have to reboot the computer, and if I forgot to save, that doubles the problem.

AE 17.1.4 (Build 37)
Mac (27 inch, late 2013) 3.5 GHz Quad-Core Intel Core i7, 32 GB RAM, OSX 10.15.7

A similar issue has happened to me when a "hardware" change happens with AE open.
Say you plug/unplug your headphones. This causes Windows to switch the audio output, but AE apparently doesn't like this and the preview stops working. Restarting AE switches the audio mapping and so everything works normally again.

This makes it impossible to use Aftereffects for my work. Very frustrating.

Similar issue here on 17.1.3
the RAM preview will stop but the whole program hangs for about 5 to 10 seconds before becoming responsive again. Doesn't matter if it's a long preview or a short one. On Windows 10 with 2x NVIDIA 1080Ti, 64gb ram, AMD threadripper 1920x

Happens in 17.1.3 (Build 41) too.

This should be the highest voted issue, as it occurs constantly—even in basic comps—and coincides often with the comp not being played back in realtime (even though it should, given the basic animation).

MacBookPro Retina 15’’ Mid 2014 – 16GB RAM – 2,8 GHz i7 – GeForce GT 750M 2 GB

same issue occurs when dragging files into a project to import. This is a very old bug dating back at least 2 if not 3 versions. whenever you try to import via drag and drop while it's running it crashes.
I bought a brand new win10 dell system used exclusively for after effects, less than 3 months old.

Please fix this bug! I have been dealing with it for months and it's incredibly frustrating.

I have a MackBook Pro (2018 i9, 32M, 1TB SSD) and a BlackMagic eGPU (560 Radeon), connected through TB3, and I can't tell you: After Effects ignores all of it. The AE is eGPU enabled, the RAM shared is 27GB and the sracth disk (SSD) has 600GB. However, the app doesn't matter about all of this, specially when there are audiotracks or short footage clips along the timeline. Preview sucks and it takes too long to work on a couple of frames.

It is very disappointing. What is it happening here?

Same here, i'm on version 17.1.2 (Build 37) and the preview is still buggy. I've restored version 16.1.3 and will be using until it's fully fixed. It makes it impossible for me to work. Here is my setup if that can be helpful: MacBook Pro (Retina, 15-inch, Mid 2015) / macOS Catalina 10.15.5 / Processor 2.2 GHz Quad-Core Intel Core i7 / Memory 16 GB 1600 MHz DDR3 / Graphics Intel Iris Pro 1536 MB

Having exactly the same issue. Been the same for the last few updates and really slows down my work flow. Sometimes have to crash the program and reopen and hope it has done an autosave. Space bar, 0, escape no use. Sometimes solve it by tabbing to another application and back again then pressing space. Running the latest version of CC 2020 and Catalina. Will try installing an older NVIDIA driver. Seems a shame to have to go backwards instead of forwards though.

Same thing. Won't stop! MacBook Pro. Catalina.

Ditto, having the exact same issue as everyone else. Ram Preview is completely unresponsive and has a mind of its own... v17.1.1 - Am using 1080ti and have tried rolling back drivers and swapping from Nvidia Studio to Game Ready drivers, and nothing seems to work.

This is the same problem of another more voted request. Please, bring your vote to there:
https://adobe-video.uservoice.com/forums/911311-after-effects/suggestions/39838078-preview-is-stuck-in-a-loop-and-is-unresponsive

This occurs only when I have any layer keyframes actively selected when I press spacebar. It loops indefinitely and I can't end the preview.

So I am using a NVIDIA Quadro P5000, downloaded and installed the new driver from 6/24/2020.
Version (451.48)

This has corrected the Preview problem in After Effects for me at the moment.

Thank you NVIDIA.

Come on guys! I work every day with this tool. Hope you'll fix it soon. Luckely for me i'm used to save constantly my progress (: but it's frustrating have to close it for this issue