It's an offer. Not a glitch. It's still available for Fiber for me. Based on recent experience. Not committing 3 months with them. Even it's half the price we are paying.
In case you guys don't get the 3 + 3 months as claimed on MyJio app, you can lodge complaint on consumer grievance forum (PG Portal) along with the evidence (screenshots showing the offer) and Jio should obliged to fulfill it.