I had been trying to use Gemini during my bout of encephalitis before treatment. I wasn't really trying to diagnose myself, but instead, was looking up side effects of the various (psychiatric) medications I was on. At the time, I (but not my wife) had thought all biological causes had been ruled out due to testing from my PCP. To be clear, I wasn't really in my right mind, so whether this was a reasonable belief or not (likely not) isn't something to be assumed. Like, I just thought I had GAD. Or OCD. Or something latent that had just all of a sudden started rearing its ugly head.
I found Gemini's reporting of side effects of medication to not be helpful. Especially because it led me to wonder if some of the things were "in my head" (without a doctor even needing to say it). Anyway, there was never a point at which any AI suggested anti-NMDA receptor encephalitis. That didn't really come up until I got into the hospital and had an abnormal brain MRI.
I've since switched to ChatGPT, which I find to be leagues better than Gemini personally.
This is all really hard to explain, so I apologize if this doesn't make a lot of sense.