From Office 365 Admin Site …
We’re making some changes to SharePoint Online pages
Plan For Change
Published On : September 14, 2017
We’re making some changes to SharePoint Online pages running the classic user experience. We’re changing the default document mode of all classic pages to be Edge mode, instead of Internet Explorer (IE) 10 mode. This change does not apply to sites that are using custom theming, or sites that have the modern list experience disabled at the site or tenant level. This change will begin rolling out Tuesday, October 1, and will complete by the end of October.
How does this affect me?
For most users, this change will just increase performance and reliability of pages. However, some custom master pages or custom web parts may contain custom code that takes a dependency on the older IE10 document mode. This change only affects the document mode of SharePoint pages. It does not require that users switch their browser from Internet Explorer to Edge.
What do I need to do the prepare for this change?
If you have sites with this kind of customization, the sites can be reverted to use the IE10 document mode by doing the following:
1. Open the site in SharePoint Designer.
2. Edit the master page that is in use.
3. Find this line:< SharePoint:IECompatibleMetaTag runat=”server” /> And replace it with:< meta http-equiv=”X-UA-Compatible” content=”IE=10″/>
4. Save the page and reload the site.
Please click Additional Information to learn more about document mode changes.