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GraphUnion doesn't seem to produce the correct result. The output should be four blocks connected in a chain, but it's not. This appears to be another bug in version 13.3.0.

Is this a bug and is there a workaround?

enter image description here

gList = {Graph[{2, 0}, {Null, {{2, 1}, {2, 1}}, Automatic}, {FormatType -> TraditionalForm, ImageSize -> {279.74999999999795, Automatic}, ImageSize -> {546., Automatic}, VertexLabels -> {"Name"}}], 
    Graph[{4, 1}, {Null, {{2, 1}, {2, 1}}}, {FormatType -> TraditionalForm, ImageSize -> {334.1249999999994, Automatic}, ImageSize -> {546., Automatic}, VertexLabels -> {"Name"}}], 
    Graph[{1, 3}, {Null, {{1, 2}, {1, 2}}, Automatic}, {FormatType -> TraditionalForm, ImageSize -> {363.1874999999984, Automatic}, ImageSize -> {546., Automatic}, VertexLabels -> {"Name"}}], 
    Graph[{3, 0}, {Null, {{2, 1}, {2, 1}}, Automatic}, {FormatType -> TraditionalForm, ImageSize -> {210.3749999999963, Automatic}, ImageSize -> {546., Automatic}, VertexLabels -> {"Name"}}]}; 
GraphUnion @@ gList
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    $\begingroup$ Same output in v 14.2.1 $\endgroup$ Commented May 4 at 14:51
  • $\begingroup$ It is better if the code is simplified. $\endgroup$ Commented May 5 at 0:57

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[...] is there a workaround?

Yes, use edge tags.

{Graph[{2, 0}, {UndirectedEdge[2, 0, 1], UndirectedEdge[2, 0, 2]}, {VertexLabels -> {"Name"}}], 
 Graph[{4, 1}, {UndirectedEdge[4, 1, 1], UndirectedEdge[4, 1, 2]}, {VertexLabels -> {"Name"}}], 
 Graph[{1, 3}, {UndirectedEdge[1, 3, 1], UndirectedEdge[1, 3, 2]}, {VertexLabels -> {"Name"}}], 
 Graph[{3, 0}, {UndirectedEdge[3, 0, 1], UndirectedEdge[3, 0, 2]}, {VertexLabels -> {"Name"}}]}

GraphPlot[GraphUnion @@ gList2, VertexLabels -> "Name"]

enter image description here

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