Lishy You sure you haven’t put a space in after the asterisk by accident?
Exactly that.
My main collaborator builds our lyric sheets and when I first import them into ST, and review a render, stray asterisks are the first thing to fix. They are always due to a space between the asterisk and the start/end of whatever text you are trying to bold.
Also make sure you haven't accidently double-asterisk'd (search and replace type error) or are trying to treat an asterisk as actual text.
Depending on what you are building your lyrics in originally, the other gotcha I run into is because we use Microsoft Word as our source (which I then transfer to TXT file and import into ST). It is easy for a stray TAB to sneak in, and in Word and Notepad is is easy to miss. I always do a quick review lyric sheets in Word with the 'Show Paragraph Marks" enabled to catch these.