I had a look through old versions and since 1.51 it has shown dates in that way. That is when we moved to a nice template for the html.
If you look in the HTML you'll see that the dates are served in YYYY-MM-DD format, it is the pretty javascript that is turning it into that other format.
Reading the code (we didn't write this code, we took it from caddy (with permission!)) I think it should be showing you the datetimes appropriately for your locale using Date.prototype.toLocaleString() - JavaScript | MDN
So you should be able to configure your browser to show you the date times how you want them.
That might be why you remember them being YYYY/MM/DD before - maybe your browser was configured differently?