If you noticed, column headers don’t always repeat on page breaks in SSRS.
Try setting the Advanced mode for the Grouping section as illustrated below, and set the properties to :
– set KeepWithGroup to After
– set RepeatOnNewPage to true for repeating headers
– set FixedData to true for keeping headers visible
Moving along, enhance the readability of the report by adding the Group textbox current value, into the Report Header.