I am a beginner working with after effects. I have done some time mapping and time reversal, but it isn't saving or showing up after I render the composition.
First, make sure AE is up to date.
Next, check your comp and your render settings. If the time remapping previews in the Active Camera view then it should render. If everything is set up properly and you are still having problems clear your cache. If none of this helps we need system, OS and AE version info down to the last decimal point and a detailed description of your workflow. A screenshot of the project with the layer that is giving you problems with all modified properties revealed (select the layer and press the U key twice) and your render settings may also help us figure out the problem.