You're hitting a limitation of Houdini Engine. The trail SOP requires input geometries from different time samples. This is currently not possible through Houdini Engine. When nodes cook inside Houdini Engine, they only have access to input parameters and geometries at a single time. So any nodes that involve getting data *outside the asset* at a different time won't work.
In your case, since “Compute Velocity” only requires geometries from previous frames, you might be able to workaround the limitation by using the Cache SOP. The idea is to have the Cache SOP store the geometries from the previous frames. So that when subsequent nodes require a earlier frame, the previous frames are available inside the Cache SOP, and the node doesn't need to get geometries from the Maya side.
See the attached asset on how to use the Cache SOP to workaround this limitation. This workaround isn't great though, because whenever your input geometry changes you'd have to clear the cache on the Cache SOP, otherwise the rest of the asset won't see the updated input geometry.
