Excel always opens spreadsheet in read-only mode I understand this issue arose over the past 2-3 years, but I haven't seen any solution.

A workbook created on a Windows PC using Office 365 - transferred to Mac (Yosemite installed) - opens in read-only mode in Office 365 for Mac.

The workbook doesn't have a "/" in its name. I made sure there is read/write access for the file and also the folder. It contains macros, some of which work, others will have to be redone.  

After saving it with a different name, I may work as usual with it like updating, saving and closing it.

After reopening it, it's again in read-only mode. 

After all this time there must be a solution for the problem.
I had the same problem. I could see the attributes set as Read-Only under the preferences but couldn't change them. I completely closed out of excel on my mac and changed the name of the excel file. That seemed to have changed the Read-Only status of my file when I opened it next. Hope this helps.