I have this bug in multiple reports where when you export a table less than half of the rows are actually included in the excel file. it looks I'm not the only one who's experienced this. I see simil...
Add this as a new measure in your fields
Row_Number =
CALCULATE (
COUNTROWS(TableNameHere),
FILTER ( ALLSELECTED ( TableNameHere ), TableNameHere[mostuniquefieldhere] <= MAX ( TableNameHere[samemostuniquefieldhere]) )
)
Then add the Row_Number field to the Table. This should add a unique Row Number to each row. Then try exporting it.