A feature is missing from the older version (as of 2019-01-28).
In the main view with all messages, whenever you encountered a threaded conversation, there used to be a way to deploy it and see what messages made up the thread. On each entry, there was a small fragment of the beginning, so that you could get a clue as to what each message was about. It was a THREAD SUMMARY OF SORTS. That was very useful to me, and saved me a lot of time and clicks at the end of the day: I could quickly decide whether I wanted to enter some thread or not (entering a thread does take some time to load, which is extremely critical when you use the Yahoo mail client as heavily as I do; on the contrary, deploying the thread in the main view was quick and seamless).

So: I have taken the time to write this up, and it would be coherent on your side to take the time to read it and let me know your position on this issue. I have complained a lot of times about this missing feature the few times I tested the beta version, and I have been of course been ignored. No answering back, no nothing.

Please, lmk asap.
Thanks,
m.