Robert:
Thanks for adding the signature.
I don't know the solution but here are a couple ideas to try:
1. Open the Label Tool Settings dialog box and go to the
Text Label panel to see what text is here. You might be able to add your text here rather than in the Label. (This assumes that you are using an Independent Label, Text Type; if not then please post your Label Settings.)
2. Alt-click on a working label to transfer its settings to the Label Tool and see if that fixes the problem.
3. If you have not done so, turn on the On-Screen Display Option for
Text Handles, seeing the Handles may give a clue to the text problem.
If none of these work, then it could be helpful to post some screen shots of the working vs non-working Labels, someone may then see the problem.
David