Parts of my project randomly appear or move. What causes this?

Recent versions of After Effects have a common bug that may cause layers or compositions to suddenly appear, disappear, or move at random moments. This can usually be solved by navigating to Edit > Purge > All Memory & Disk Cache. This will not affect your saved changes. If this isn’t the issue, it might just be a result of previewing in less than [Full] Quality, which will sometimes produce strange glitches.