@Smurfhunter I too had this issue - turns out the flic buttons were being added to a room called 'default room' which is only visible when clicking in the home app on the three dots in the upper right. Scroll down and see if you have a 'default room' as well. I have no idea why or how they get added there.
More frustrating too is when you do see them there - they are arbitrarily named flic and some numbers. This is an issue if you choose to add a few buttons to HomeKit at the same time. Then you have zero clue as to which button is assigned to which name!
I sure wish Flic responded better to these questions. Such a great product but they need to be more involved with their users.