To resolve this issue, add the SharePoint Online site toTrusted Sitesin Internet Explorer. To do this, follow these steps:
On theToolsmenu in Internet Explorer, clickInternet Options.
On theSecuritytab, complete one of the following actions:
For private sites that use https authentication, selectTrusted Sites, selectSites, and then add the SharePoint site to the trusted sites lists.
For public sites that use https authentication, selectLocal Intranet, selectSites, and then clickAdvanced. Add the
SharePoint site to the trusted sites lists.