Date column timeline inconsistent display in Line Chart

Hi experts,

   I have learned a bit of Dax and Power Bi over the course of last month and wrote a bunch of aggregations, but stumbled accross something odd that I can't explain and I feel I need some help.

   I have two pbix files, created measures are similar in both, one for sales one for purchase.

   I need to display a line chart with month/year at the bottom and some aggregated values as lines for each item.

   Everything works well up to the point of the dates displayed on the X axis, I use a column in each file and add it on the Axis section of the Line Chart. I also removed the hierarchy and only display the new column.

    Here is how the visual looks in file 1, the way I want them to look (month, year): 

     This is how it looks in file 2 (it seems it shows a day/month,hour):

   Formulas/formatting for both of these are the same, as it is the underlying original field formatting, first file column:

 second file column:

   Do I have to format the date in a certain way to force it to be month/year for both of them and what is the best option?

Cheers,

Robert