Switching between the built-in "Text and Background Colour" schemes changes the "Text colour" and "Background colour", but has no effect on the "Bold colour" which defaults to black.  If you have turned off "Use colours from system theme", have selected a built-in scheme with a black brakground, and haven't configured a bold colour manually (so it defaults to black), and have accidentally turned off the "Same as text colour" option, then any bold text will be invisible. This happened to me for a few days until I noticed the "Same as text colour" option wasn't selected.

Would it be possible for the built-in schemes to update the "Bold" colour in addition to the "Text" and "Background" colours?

I'm not sure what the bold colours should be for the different built-in schemes. Several of them could just set the bold colour the same as the text colour, especially when the normal text colour is black or white.