What does your Task look like?

Alex is asking the right first question: the exact Task Scheduler setup matters.

A few things I would check:

Make sure the task is launching the full path to MSACCESS.EXE, not just the database file.

Make sure the database path is in quotes.

Make sure the "Start in" folder is set to the folder where the compactor database lives. Access can behave differently when launched by Task Scheduler because the working folder may not be what you expect.

For testing, set the task to "Run only when user is logged on." Access is a desktop application, and running it in a hidden/non-interactive background session can sometimes hang if there is any prompt, trusted-location warning, missing reference, linked table issue, security prompt, etc.

I would also add a simple log table or text file to the compactor database so it records each step: startup, beginning compact, finished compact, and quitting. That will tell us exactly where it is getting stuck.

And finally, make sure the compactor database actually closes Access when it is finished, for example with DoCmd.Quit acQuitSaveNone.