It's funny that after your post I also encountered this, although before that everything was fine.
Here if you look the author of the scene used everything possible, rotator, piston folder with linked nodes, turning bones on and off in NodesConstain.
In short, it's total chaos, honestly I won't even try to figure out how it works, but it looks like a skyscraper held together with tape.
The problem starts at the stage of disabling IK and FK and re-enabling them. If you add nodes to the character, you can see that the character should animate, but during disabling at 00:43.16801 and re-enabling, the bones break, so the scene starts over and nothing happens.
I would not waste time trying to solve this problem because of the 3 seconds of animation, but simply changed the duration to the moment where the bones are disabled by setting the "Enable" status in Ik enable and FK.
There is also a possibility that the author made the scene on an old build without additional plugins and therefore everyone who updates their builds has similar problems. The situation is similar to if you launch scenes with animations from the year 2019-2020, your scene will be broken with a 95% probability.