Summary Lines Not Bold

Correction: None of the Fields are turning bold on new Summmary Lines and even on the old Summary Lines, some fields (such as UID) are suddenly not bold.

Assuming that you are "in" the Gantt Chart View, the fast way is just to overwrite the current Gantt Chart View with a fresh one from the Global Template.
Make sure that first you are in a View other than the Gantt Chart View, then Tools, Organizer... and copy the Gantt Chart View from the Global Template to your project.

If you want to keep the View that has the bad Summary formatting, then first copy it and give it a name like "AA Gantt 1". To fix this one, just try re-setting the Text Styles.

Everything to do with the Formatting, Text and Bar Styles, Layout and Page Setup is stored in the View.
You are better off not re-formatting the Gantt Chart View in any way, keeping the original clean, so that you can always return to it.
If you want to change formatting, Layout or Page Setup, make a copy of the Gantt Chart and change that instead.

If you have various sets of formatting, Layout and Page Setup, for example for different purposes or audiences, have corresponding Views for each.

Worked like a charm. Thanks!