Apple recently updated their video software in the latest version of macOS Catalina, transitioning from 32-bit to 64-bit. With these changes, they dropped support for some common and standard video codecs. Photo PNG + Alpha is no longer supported in any form, and all but one of the Motion JPEG variations are still supported (MPEG - OpenDML).
For this reason, Photo PNG and Motion JPEG is no longer supported across VideoHive & Elements (more info on this subject to come shortly). We detected an issue with items submitted through StockSubmitter, when authors use the software to downscale 4K footage to HD resolutions. The software was taking a 4K Photo JPEG input, and rendering out 1080p Motion JPEG videos.
StockSubmitter has assured us that the issue has been resolved, but will require authors to perform an update on the application to see this change.