I've got an issue when using spacebar for preview. Sometimes, even though there is space on RAM and the program can cache the preview easily, something goes wrong, and instead of starting to cache the data for preview, After Effects does nothing and on spacebar or numpad0 press goes back one frame. Meaning when i press spacebar or numpad0 for RAM preview, AE doesnt start rendering, it just moves the timeline position one frame backwards and one more frame with every press of spacebar/numpad0. It will continue to do this until restarted. I'm running Ae 18.0.1
I ask for urgent help
Sorry, but that's yet another useless post. You have not offered any system information, actual preview settings, details about the contents, your cache settings and so on. Just saying that it misbehaves is not telling us anything.
Show us with a screenshot where we can see all your interface included the Preview panel and the Timeline, or better if you can make a video capture of your screen, to try to help you.
Try updating GPU drivers. If not, try from menu File / Project Settings... / Video Rendering and Effects tab, try changing GPU acceleration to another in there.
There are other user posts here on a similar issue. If your need is urgent, I'd recommend searching for your issue and seeing if any of those solutions work for you, which may be faster than us starting from scratch troubleshooting you. Good luck!
I haven't found a solution yet.
Sorry for your issue. Have you tried resetting the preferences? Here's how: https://community.adobe.com/t5/after-effects/faq-how-to-reset-trash-preferences-in-after-effects/td-...
If that doesn't work, try updating After Effects to the latest.
Let us know how it goes.
I updated to the latest version (18.1) and it's running ok, so far.
Try to upgrade your GPU driver.