mac mail 11.1: view reply from inbox

High Sierra latest updates; Mac Mail 11.1

I used to be able to click on the left-pointing arrow on a message in my inbox that I had replied to. Doing so would bring up my reply (although not necessarily the latest reply, if there were multiples.)

At some point in the recent past that stopped working. The left-pointing arrow still appears but clicking it does nothing.

Is anyone else experiencing this?

Does anyone know of a fix for this useful, but now missing option?