TypeError: Cannot read properties of undefined (reading 'spanID') / Span Relationships Errors

Reported in: https://raintank-corp.slack.com/archives/C01UMS158LF/p1747179587464969 > Any ideas why we would see the following error when querying traces: "...TypeError: Cannot read properties of undefined (reading 'spanID').." Initial investigation: > The span A has no parentSpanID so it's the root span but has a reference to B which is also a child of the trace. From the frontend perspective: We treat span references as "follows from" type of reference ([code link](https://github.com/grafana/grafana/blob/37dbf037de548e1e855c0a59697769d20a8b5b65/public/app/features/explore/TraceView/utils/transform.ts#L46)) but if I understand correctly the reference should never be a child span (or any span in the future). But in this case we have a root span with a child span reference. This creates a cycle of dependencies and causes the visualization to get confused how to build the tree structure/hierarchy and it's a use case that we don't handle specifically as we don't expect it to happen. > The issue in the frontend seems to be that the root span is marked as a span that also follows from its child which creates a cycle root -> child -> root -> child ... and the visualization doesn't handle that case. To be clear: in fronted have 2 ways to create references between spans: CHILD_OF = "parent / child" (hierarchical) relationship defined by setting parentSpanId property in the span (a span can have only one parent) FOLLOWS_FROM = "follows from" (casual) relationship defined by a list of spans that We assume "follows from" spans happen in the past, not in the future. In our case the root span has "follows from" linked to a child. The child is a span in the future, not in the past. Frontend code takes all span "references" and marks them as "follows from" [here](https://github.com/grafana/grafana/blob/37dbf037de548e1e855c0a59697769d20a8b5b65/public/app/features/explore/TraceView/utils/transform.ts#L46). Those "references" are Span.Links coming from Tempo (mapped in Grafana backen…