Was having this same issue with SSRS 2017 and finally found a way to make it work. Took a lot of trial and error and would hope to save someone else the pain that I went through.
For the Tablix I set Repeat row headers on each page to true but repeat column headers to false.
Then on the advanced settings for the group headers set Keep Together = true, Repeat On New Page = True and Keep With Group = After
Finally on the Advanced side for static column headings I set Keep Together = true, Repeat On New Page = false and Keep with Group = None