"an issue on" implies: "a matter on the topic of" and for that reason can only be used when one can insert the phrase "the topic of" after the "on", while "an issue about" can utilised right before something. Stack Exchange network includes 183 Q&A communities which include Stack Overflow, https://onlybookmarkings.com/story19900813/the-fact-about-hoodies-exporter-in-pakistan-that-no-one-is-suggesting