I also had the same problem. The only solution I found, for the time being, was enabling the live message edge screen panel and then I had full access to the application as I would clicking the regular button on the keyboard.
I personally would try to swipe open your edge bar, then on the bottom, you should see from left to right a settings wheel some .... and something that will look like stacked "•-" or a hamburger menu with • in front of each line, tap on those and it should pull up a list of edge screen options you have installed on your device. Look for the Live Messages. You could possibly tap on it from there or you'll have to go back to where that settings wheel was I previously mentioned and make sure you've select Live Messages to add and to customize your different edge panels.
I hope that helps you. I'm not the greatest when it comes to explaining this kind of stuff since I'm sure there's plenty I'm doing wrong and don't know how to do.
I hope this modified fix works for you and sooner rather than later or not Samsung will bring back a Live Messages icon within the Samsung SMS messaging app that comes with the device especially since this isn't a problem we're all complaining about while using some third party messaging app.
If you find any remedy to this issue other than the one I've mentioned previously please share with others in this thread.
Thank you and take care
I check my edge panel and just a few random apps. They have it on the play store and downloaded it and pay a dollar or so to remove the watermark but it's not linked directly to the messager. You have to hit share and click on the person's name...ugh
I just did my update today for my 10 plus and my live message icon is gone and Iwant it back.I have all the ones I created but cant make any new ones. Ugh updates
When you open the Live Messages from your Edge panel you should see where it shows Live Messages and you'll want to select that to create new ones.