I would expect COUNT and COUNTBLANK to calculate the complementary rows within a column: non-blanks values versus blank values.
Therefore, COUNTROWS = COUNT + COUNTBLANK.
Both null value and empty text string value should be considered a Blank value by both functions.
COUNTBLANK considers both null and empty value as blanks.
COUNT considers only null value as blanks.
The following Table with a text field has an empty string value and a NULL value.
I have reported this issue internally: CRI 135118692. Will update here once I get any information.
Best Regards,Qiuyun Yu
This is by design. This is how Excel functions were designed and DAX inherited the behavior from there.