There is a memory-related bug in the version of Safari included with iPadOS/iOS 13 through 13.3.1 that causes many videos to fail to load in Vernier Video Analysis (VVA).
The problem is increasingly apparent with later releases of Vernier Video Analysis as the app has more features and uses more resources. As of version 1.3 of VVA, few videos will open in the app when using these older versions of the operating system.
Version 13.4 of iPadOS/iOS resolves this memory issue. Update devices to 13.4 for use with Vernier Video Analysis.