Yes, I noticed this too. I had it build a MongoDB aggregation where documents would get aggregated in hourly timeslots (compute temperature averages+hi+low for every hour). Two ways to do this: 1) convert the datetime to a YYYY-mm-dd-HH string and use it to group the documents, or 2) use a Unix timestamp and do some math on it.

I was already using 2) in some projects, so I wanted to check if it was able to do this.

It first suggested 1), then I told it to make it more efficient by avoiding strings so it gave me 2). Wow.

That was around 3-4 weeks ago. When I tried it again this week, it would only output 1) and it wasn't able to make the move to 2) anymore by telling it to not use strings. It kept using them.