Code
T5105 called-too-deep
A flow was called from a run that stands as deep among the runs that called each other as the project allows.
Details
A flow that a step calls starts a run and waits for it. Such runs stand three deep where the project states nothing: a run, one it calls, and one that one calls. The call of a fourth fails with this code, and no run is added for it. start, which does not wait, is not held so.
The fix
Start the flow with start where its answer is not needed. Where the runs must truly call each other deeper, raise the limit: limits: { callDepth: 5 } in project.