I would check the plugin itself before changing anything in the SAML configuration.
First, open its manifest.xml and check the minSystemVersion / maxSystemVersion. IIQ plugins can declare the IdentityIQ version range they allow. SailPoint plugin documentation
If 8.5 is within that range, check the UI snippet that loads headerInject.js:
Confirm the plugin is enabled under Settings → Plugins, or with plugin list / plugin status *.
Check the snippet’s regexPattern and, if present, rightRequired. The URL must match and the logged-in user must have the required SPRight for the snippet to render. Plugin manifest documentation
In browser DevTools, confirm headerInject.js is loaded and has no JavaScript errors.
If it loads but the Signout entry is still missing, compare the selector in headerInject.js with the 8.5 header DOM. This plugin uses that file to inject the logout menu entry. Related Community example
I would not assume an 8.5p1 incompatibility yet. First confirm that 8.5 falls within the plugin’s allowed version range and whether its UI snippet is actually being injected.
really thank you very much. I’ve solved the problem with your ‘troubleshooting guide’. My problem is that I was very optimistic. I inserted code so SailPoint translate the ‘sign out’ text to every language. And that was breaking the code.