The Error message returned itself is incorrect. Generate Org chart data is available in the Set node. However it is data from input 2 - Generate Table Object that is not accessible in the Set node after merge.
The complete workflow cannot be shared due to privacy constraints regarding data. The below is WF from V 1.26. Tried V 1.28. Does not work either.
Does the node not provide any pairedItem data. How to provide it, is documented here. That said, in this case, it should not be needed as no node before those nodes is referenced.
It looks like you do not want to use the Mode: "append" but rather Mode: "Combine" & Combination Mode: "Merge By Position". Currently it will create two different items. For each, only one of the expressions can be resolved, as one item can only be resolved for the “Generate Org chart” node and the other only for “Generate Table Object”. Meaning it will always error. From what I can see of your workflow, I imagine you rather want to have a single item that consists of the data of both incoming nodes. Once you change the mode as described above, the outgoing item consists of data of both inputs and is so able to resolve correctly.