I use several Excel spreadsheets stored on our company's internal SharePoint site. When I open these in Excel ("Edit in Excel", not the Excel web app), then click the Refresh button at the top, it no longer refreshes as normal. What happens is that the Save As menu appears. If I save as a new file with a new name, it saves correctly. My other choice is to overwrite the existing file, but this doesn't work. After the overwrite, if I click on the file name at the top of Excel and click Version history, it does say I just saved the file. If I exit, then on the SharePoint page, the "Modified" column also correctly updates. But when I reopen the file, the changes I made and thought I saved don't appear.
This problem started two days ago. My work has Microsoft Office 365 ProPlus and my Excel is Version 1805 (Build 9330.2087). My computer is running Windows 10 Pro, Version 1703, OS Build 15063.1088.