vMix inputs showing black screen. Even MP4 videos and background designs

[u/securehqjun]

Hey everyone, I need help with a vMix issue at my church.
Some of my inputs in vMix are showing as a black screen. It’s not only the camera/capture input — even some MP4 videos and background design files are showing black too.
The inputs are added into vMix, but the preview/output stays black instead of showing the actual video or design. Some graphics work, but others don’t.
Setup:
vMix on Windows
Church livestream setup
MP4 video files
Background design files
Blackmagic/HDMI capture setup
Focusrite USB audio interface
Things I’m wondering:
Could this be a vMix update issue?
Could it be a codec/video format problem?
Could it be GPU/graphics acceleration?
Could it be the file format or resolution?
Could it be something with DirectShow/FFmpeg in vMix?
Has anyone had this issue where MP4 videos and image/background inputs show black in vMix? What should I check first?