File size limit is set initially for the Document API to 50MB. This applies to documents managed through Document Management and users can manually add a document that is 50MB in size. Web services, such as Document API, can only handle 26MB though - and that includes buffer size. For downloads from external systems, such as UniGroup, this limit also applies; however, many of these systems only support a certain size file, such as 5 MB on files from UniGroup.
Additionally, the amount of RAM available on your system may not be sufficient at certain times, especially during peak usage times, to handle large files or groups of files being added at a single time.
Files made available to the MSCrew mobile app should also be limited in file size to avoid loading delays.