Using more than a single break struct node in sequence (despite no break nodes performing calculations) disables fast path. Splitting structs instead does not cause this issue.
Create a struct containing a float.
Create another struct containing the previous struct.
In an animation BP with the outer struct as a variable, use the float in an animation node by breaking both the outer and inner structs. Notice how the fast path is disabled.
Now use the float by splitting one or both of the structs instead. Notice how the fast path is enabled.
Expected: As long as none of the break nodes are doing calculations, using them in sequence should not disable fast path.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-71226 in the post.