Sorry for going off topic here but I've had the same experience.

I'm not sure which update improved 4o so greatly but I get better responses from 4o than from o4-mini, o4-mini-high, and even o3. o4 and o3 have been disappointing lately - they have issues understanding intent, they have issues obeying requests, and it happened multiple times that they forgot the context even though the conversation consisted of only 4 messages without a huge number of tokens. In terms of chain-of-thought models I prefer DeepSeek over any OpenAI model (4.5 research seems great, but it’s just way too expensive).

It's rather disappointing how OpenAI releases new models that seem incredible, and then, to reduce the cost of running them, they slowly slim these models down until they're just not that good anymore.