Spreadsheet lost month of work - wrong version update from dropbox?

[DaneOfTheHill]

I start my workdays clicking on the top spreadsheet under "Recent" in excel (my companies current book). Same today, everything is fine. Closed everything and restarted computer (because Windows' File Explorer didn't open). Open the same top option in Recent, now the spreadsheet is like a month old (lots of data missing). This is devastating, really hope someone can point me in the right direction.

I use dropbox to back up the file, never had this problem before. Any ideas where to start with the troubleshooting?

Windows 10
Wi-Fi connection
Microsoft Office Professional Plus 2016
Desktop computer
No other problems, systems runs smoothly, only Firefox, Telegram and Spotify open apart from Excel.

[DaneOfTheHill · Accepted solution]

Update: I found the old version in "Sync history" in Dropbox, seems there was a circular reference and therefore the up-to-date version had been saved as "conflicted copy".