This is a very counterintuitive issue. I assume it’s a bug but maybe it’s designed this way for some odd reason.
I have Prefabs made using an imported FBX. The Prefabs have SequenceAsset components to be used in Sequences. But I get an exception after the project reloads that “Prefab is not a Sequence Asset”, even though all the Prefabs I had added to the Sequence Assets window do have that component.
After modifying the package to tell me which asset was the issue, it spit out the FBX that those SequenceAsset Prefabs derived from, even though I never assigned that FBX to the SequenceAssets window, so not sure why it’s trying to touch it at all.
Sequences 2.0.1/Unity 2022.2.1f1