Hello Teresa-18,
Welcome to the Microsoft community.
May I get more information about your current problem so that I can better help?
- I would like to know what version of PowerPoint you are using, and you can refer to the following steps to find the specific version information. If it is convenient, can you share a screenshot of the product information screen with me?
- Open PowerPoint application and select Account.
**Note:**If you don't see Account or you already have a file or document open, choose File from the menu, and then select either Account or Help from the list on the left.
- Under Product Information, you'll find your Office product name and, in some cases, the full version number.

- According to your description, the situation only happens in some files, so I would like to know if there are some similarities in these files. Could you increase or decrease the text level in a newly created PowerPoint document via option 1?
In my test, I found that when you add numbering to text in PowerPoint, the option 1 you mentioned works. But if it is normal text, i.e., if the text is not numbered, option 1 does not work, you need to select a line of text and then it will work. So, I would like to know if the problematic PowerPoint documents are because the text are not numbered? Could you share the problematic PowerPoint document with me so I can test it?
You can send the PowerPoint file via private message through the Messages link at the top right of the page.

Looking forward to your reply, we may need to go through some testing to find the cause of the problem.
If there's anything that's not clear, don't hesitate to let me know.
Sincerely
Mavis - MSFT | Microsoft Community Support Specialist