Microsoft Word on MacBook Pro: Tab problems
There is an old trick I learned on a help desk well over 10 years ago which USUALLY still works.

In the problematic document, turn on paragraph marks. It's in the ribbon under "Paragraph." or Press COMMAND-* (Mac) or CTRL-* (PC) [EG SHIFT COMMAND/CTRL 8].

Select All in the document. Use the edit menu or click in the document and COMMAND-A (Mac) or CTRL-A (PC).

Scroll to the bottom of the document and locate the very LAST paragraph mark at the very end of the document.

Press the shift key and click just to the LEFT of the last paragraph mark, thus de-selecting it.

Now everything in the document is selected EXCEPT the last paragraph mark.

Release the shift key, and tap COMMAND-C (Mac) or CTRL-C (PC).
Create a new empty Word Document.

Click in the document and paste what you just copied from the old, problematic, document into the new one. Save the new document under a different name and see if your formatting/behavior issues have gone away.

When I learned that trick I was told that MS Word stores document formatting in the last paragraph marker. Regardless of whether that is true or not it will often fix problematic MS Word documents.