Ah, I see. You reproduced this issue:
You can try to use this command to see your bucket
uplink ls --recursive
The short explanation - you have created a bucket with an empty name and path testfilezilla inside. I would assume that there are some files (because you can’t create a prefix without an object).
And this can be easily reproduced, since the FileZilla is offering to create a folder in a format /new folder. Such a format creates a bucket with empty name. But I wonder how they keep the prefix then.