You are right, this error message was recently introduced and its function is to notify the user that the series' X value does not need an expression, when using a category scale. As explained here
, the X value will be automatically determined by the category group, which has its Grouping set to a certain field, so it's redundant to use this field also for the series' X property.
Please make sure that the field used for category grouping is LapSeconds
and remove (reset) the X property from series definition. This will allow the graph to be correctly processed and rendered.
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