UPDATE (October 2022): most recent guide to our integration/embed codes: Filemail Integration v3 guide | Filemail.com Help Center
We observed that some CMS platforms (SquareSpace, WithoutCode, possibly others too) use dynamic page loading which might cause trouble during the initialization of Filemail integrated downloader or uploader. Most often the problem is that the integrated component doesn't load during page navigation.
The solution is to use a separate container for the integrated component:
Note the wrapid parameter in the script URL which must match id of the div that should contain the integrated component. Also note that if you are planning to integrate multiple components on one page those ids must be unique for each component.