For all of my groups, the prefix is a color code and the bold color. The color does show up but the bold does not. Example: &a&l{Owner}.

What chat plugin are you using? EssentialsChat? DeluxeChat?

Is vault up to date? Is luckperms up to date?

Did you set a prefix earlier that wasn't bold?

All of above ^^, plus:

• Does the correct value show when you run /lp user <you> info
• Try with /lp user <you> meta info - is that prefix at the top of the list?