Sometimes, you can experience wrong/strange sortings of your textual data in the semantic model. This is caused by the collation of the Power BI Premium endpoint not being set to what you would usually do in your geography had it been a regular tabular analysis services endpoint.
According to this: https://data-goblins.com/power-bi/case-specific it should be possible to change the collation – although not through the standard interfaces, but only through Tabular Editor or directly editing the file. I would like to see TimeXtender added to that list.
