I'm trying to use flow variables for the lower bound and upper bound fields under "use range checking" in the "include rows by attribute value" mode of the "Row filter" node. However even though I can select the respective variables (I think I defined them before correctly) for "lower bound" -> "datacell" and "upper bound" -> "datacell" under flow variables it tells me "Invalid Settings. Specify at least one range boundary".
Within the Flow Variable tab please expand the org.knime.core.data.def.DoubleCell (below your selected option) and select the variable for the DoubleCell item.