MatLab 2018a boxplot

I am having a major issue with 2018a compared to 2017b when I try to generate boxplots by grouping variables.

I have organized my (g) grouping variables into a string matrix (2 columns and variable number of rows, see attachment "group_string_variable") which I plot against the distributions (see attachment "vector_data") to visualize as a boxplot.

To generate the boxplot I use:

boxplot(vector_data(:,1),group_vector_string);

This works well in MatLab 2017b BUT in 2018a I get the error:

"Error using boxplot>convertToCellarrayOfColumnVectors (line 1004)
'G' cell argument must be a vector

Error in boxplot>straightenX (line 910)
[gDat, gRows, gCols] = convertToCellarrayOfColumnVectors(g,'G');

Error in boxplot (line 274)
[xDat,gDat,origRow,xlen,gexplicit,origInd,origNumXCols] =
straightenX(x,g);

Error in Analysis_Elecropherogram_total (line 171)
boxplot(vector_data(:,1),group_vector_string);"

Can anyone help me figure out why the newer version of MatLab crashes? By looking into the documentation it looks like that nothing should have changed for organizing data in the boxplot.

Thank you!

Eugenio