There are sometimes problems with using SyncTeX to jump from the preview to the source window when certain packages are in use.
In these cases, if you try to double-click the preview or use the arrow buttons that sit on the divider bar between the source pane and the preview pane, an error message will be displayed:
Couldn't find the corresponding source file.
This is known to happen in documents using the TikZ shadows or fadings library. The todonotes package also loads the fadings library, so may also cause SyncTeX to fail.
If you see this error in a project where you're not using TikZ shadows, you can send us a support request and we can investigate further. Note also that the main .tex document of an Overleaf project should be in the top-level of the project (i.e. not in a folder) for SyncTeX to work.