Column headers disappearing after merging of rows using the group by functionality

Good day my beloved Power BI community

I am having a huge challenge when I am merging rows using the group by feature. I am a beginner to say the least but I do attempt to get dirty with with the addictive BI. To make matters worse, I have to use the M language which I do not know eg being forced to use the Text.Combine instead of the List.Sum of non-interger value. At the end, I do merge rows but at the expense of losing column headers. Anyone been here before?