Did you copy it from an external text editor (e.g. MS Word) or wrote it directly in Signavio Editor? We can't guarantee that a text format from an external tool like MS Word would be correctly applied to Editor and Collaboration Hub.
A simple solution for this case would be to copy the whole text of the attribute in a plain text editor (Notepad, Edit) and paste it again in Signavio Editor. You can afterwards use the format options in our Signavio Editor.