BigTable - large rows (more than 256MB)


We are using JG on top of Bigtable. While trying to understand some slow queries, I found the following in the Bigtable query vizualizer: "Large rows — Found 1 single key storing more than 256MB."
Not sure I fully understand the data model, does this mean that we have a single vertex which is very large (maybe a supernode)? Or does it mean we have too many vertices with a given label?
How does one begin to understand how to approach this?

Many thanks in advance,

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