In InDesign file, we used Mathematical pi opentype font for math operators such as +, -, / etc.,
In this case, accidentally we used ornament slash (Unicode: 2219) in one of the occurrence instead of division slash (Unicode: 2215). Since both characters are looks similar.
In Mathematical pi font, there are 2 kinds of slashes are available. One is division slash ( / ) and another one is ornament slash.
The input character for the ornament slash is bullet, display character is slash. And for division slash, both input and display character is slash.
Concern: Unfortunately, the slash is displayed as bullet (I.e., input character) in export pdf. In PDF compare (text difference), it checks the input character of the PDFs and does not show as error.
Since it is not a reproducible error. It happens in rare cases.
In Mathematical pi LT Std font, there are so many characters are same like this. (i.e., displayed similar but the input character varies). If any character looks similar were used in InDesign will affect in PDF as happened for slash. Anybody please suggest how to ensure the quality?
That's actually a normal slash, not "ornamental". Did you type it with the keyboard?
Something else: I disadvise to use a slash as a symbol for mathematical division. Use the common symbol ":" or "÷". A set of mathmetical symbols are included in standard fonts like Arial.