Actually - digging into this, I now realize that this is probably not a size limitation, but rather a cyclic reference issue. Apparently, at a certain size, my graphs reach a point where there are (in-direct) cyclic references, causing the sankey diagram to break.
I searched around and it seems that in D3, they’s already solved this limitation and there are a number of gists with solution to this problem. Any chance to see a porting for these solutions to plotly?