The button name is stored on the button itself, so that you can see the same name when you connect the button to another device or app.
As mentioned here: https://github.com/50ButtonsEach/flic2-documentation/wiki/Flic-2-Protocol-Specification#get-and-set-name, the name is maximum 23 bytes.
This has been the case for a few years. Before the name was only stored locally in the phone (or hub) and then this restriction was not in place.
I suggest you to use a shorter name, e.g. prefix it with "s:/" and then add the IP address of your soundbar.