Formatting issues in Word Microsoft 365 Copilot online.

I am experiencing formatting issues in Word (Microsoft 365 Copilot online). I am a student, and I have a problem formatting my thesis in M365 Copilot after previously working on this file on an older device with an older version of Word.

I recently purchased a new laptop, where I no longer have access to that same version of Word. My only option now is to use Word in the browser. However, the file that formatted correctly on the old device is now not formatting properly.

The automatic table of contents is breaking. After clicking “Update,” Word assigns random page numbers, most often all entries show as page “8,” or, for example, the “Introduction,” which is actually on page 3 (I manually set page numbering in the old version), suddenly appears as page 5 in the table of contents. Every chapter and subchapter is shown as being on the same page, usually page 8. The formatting options and capabilities also seem worse compared to the interface of the older version.

The same issue occurs on my student account. Please help, I am currently writing my thesis.