Hi @geepy,
I also think the way the relayoutData values are changed when interacting with a dcc.Graph might make it difficult to use in callbacks and posted a somewhat similar question. In that case, a promising answer by @worker1 was to use State(‘graph-figure’, ‘figure’) instead. In the resulting dict, the range values of the figure are also found (e.g. figure[‘layout’][‘xaxis’][‘range’] for the x range), and, as far as I know, the structure of the returned dict is independent of the user interaction method. Does this approach work for you?