Our arcgis enterprise portal 10.9.1 went down one after another within couple of weeks with this symptom below. Our landing page, information bar in the arcgis portal changed suddenly where we were no longer seeing the usual tabs. We could still sign in, as windows user and also as Initial Administartor Account, however the headers showed different things like Pricing etc, screen shot below.
Before this happened, it looked like this below
When this happened in Dev environment, we thought it could be because the certificate had expired, but in test, it happened and the certificate has not expired yet. When this behaviour was seen in test, we reached out to esri support immediately and during troubleshooting, we stopped and rebooted the portal service and thats what broke the portal as the postgres was not able to start at all after that, same as what happened in our dev environment. java.exe and javaw.exe can't start, only portal process starts. But the symptom was our information banner on the home page/landing page suddenly updated without us doing anything.
If you have seen this behavior and have a resolution, please kindly share.