I'm using v3.0. I have a scene that I've added Mixamo characters in various running or walking animations. I have zero experience rigging or animating figures, but managed to get everything working great in the scene. I switched off the collections with the people to work on and render other elements, but when I went back to them ALL of my humans were now displayed in T pose. I see the animations and keyframes in the outliner and timeline, but all are now in T-pose and no animations play. Is there a single global switch somewhere that would do this since I didn't touch any of the dozen or more people (let a alone ALL of them)?
Another possibility might be one of the many crashes I experienced (that's another story) that rendered my project file unopenable (even when switching out the .blend1 file). I found that I could open the file with an earlier 2.93 or alternate version (e-cycles or K cycles), then resave. This would allow me to open in v3.0...but might this remove something from the animated humans? I discovered this recently when using the "holdout" switch under object properties - something missing from v2.93.