Android Marshmallow changes quite a few things for the devices which have the software, not all of them major changes of course. While Google's tweaks and alterations to the software have usually been for the better, change isn't always a good thing and that seems to be the case with one feature that users are a little upset over. In particular, the sound search widget. While the app still lets users identify songs, the history is no longer easily viewable by means of the app like it used to be thanks to the recent updated version with the coming of Marshmallow, however, it's also important to note that the biggest change only affects those on Marshmallow and not on previous versions of Android.
For users that are on Android 6.0, the sound search widget no longer saves the music searches in the history log to be found later on, which means users will need to make note of the identified music right then and there. This only happens with new searches though and not old searches, which can still be found in the search history online. Furthermore, users on previous versions of Android still have the ability to see searches in their history online whether new or old. Although not capable of saving new searches to the history anymore, the widget does have a new look that's more in line with the Marshmallow and material design style so it's at least more visually appealing than before.
It's understandable that users might find the lack of saved searches to be a hindrance, so it's a wonder why Google removed the function in the first place. That said, some users may have never really used the sound search widget in the first place, or enough for this change to make any difference to them. For those that used it quite a bit and are finding it hard to get by without the capability available to them, other alternatives like Sound Hound and Shazam still do the trick, and both are free apps with widgets to do the exact same job so there's at least some way to identify songs and keep them stored in a log for viewing later on.