1. I purchased the Pro x5 plan at 12:51 a.m. on April 24, 2026, and was using it.
2. For some reason, while the Pro x5 plan was active, I switched to the Plus plan between approximately 11:00 a.m. on May 23, 2026, and 12:30 a.m. on May 24, 2026 (No payment had been processed by that time.)
3. I noticed that I had been switched to the Plus plan around 12:50 AM on May 24, 2026.
4. Upon seeing that my Codex usage had dropped to 0%, I repurchased the Pro x5 plan at 1:03 AM on May 24, 2026.
5. On the ChatGPT plan change page, I paid for the Pro x5 plan using the remaining balance from the Plus plan.
6. However, the Plus plan had not been billed at that time, so I purchased the Pro x5 plan for about $20 less.
I neither anticipated nor exploited this behavior; I am writing this post to report the bug.