EXCEL stopped allowing multiple users editing spreadsheets live, Word still works.

I've been using 365 and group sharing of document via OneDrive group drives through my organisation.

The tools allow multiple users to open MS documents/spreadsheets directly from the OneDrive shared group drive and allow those users to edit the file at the same time.

Word & Excel worked for quite some time, however a for about 1-2 months Excel spreadsheets have stopped allow this live group edit to work. This means when a user opens a spreadsheet that is currently open, it must be opened in READONLY mode. Word still allows multiple users as stated.

We open the file from the group drive by >RMB>View online>opens in a browser>Edit in Excel> Message: This file is already open ...