When accessing Portal for ArcGIS 10.4 in Internet Explorer (IE), enabling Compatibility View in the browser causes IE to display a runtime error when accessing the main links at the top of the page, such as Gallery, My Content, and so on.
Remove the portal site from the Compatibility View list, and uncheck both the 'Display intranet sites in Compatibility View' and 'Use Microsoft compatibility lists' options in the settings.
Or
Update the web adaptor's web.config file. At the bottom of the web.config file, there is a section that starts with <system.webServer>. Add the following after the open tag for <system.webServer> as follows:
<system.webServer>
<httpProtocol>
<customHeaders>
<clear />
<add name="X-UA-Compatible" value="IE=10" />
</customHeaders>
</httpProtocol>
</system.webServer>
Essentially, any workflow that injects the IE version that the web adaptor should be compatible into the header to address this issue.