The 9892 has a CTR of only 15-30%. After 5-10 years, this drops. If your output voltage never goes below 2V, replace the chip.
Your circuit is not working. The 9892 is suspect. Use the datasheet as your diagnostic checklist: my 9892 datasheet
In the heart of a bustling tech hub, Elias, a senior engineer nearing retirement, sat before his terminal. On the screen was the "9892"—a project he had nurtured for nearly a decade. While younger colleagues saw it as a set of voltage limits and thermal tolerances, to Elias, every line of code and every schematic was a memory of a problem solved or a breakthrough achieved late at night. The 9892 has a CTR of only 15-30%