It comes from my objective experience and from that of dozens of users reporting it on Reddit. It's easy to dismiss one person but when dozens are reporting it, there could be something to it.

Could it still be a mass hallucination? It's possible but unlikely.

It also is no surprise that 6-Sol costs as much as 5.6-Terra. Is this mere coincidence or meant to reflect a certain computational cost? I fear the latter.

In any event, third party benchmarks (not conveyed by OpenaAI) should help. We know the joke of how OpenAI distorts the Y axis in plots to misrepresent model performance, although in this case the reality is likely worse.