Your UIA mappings are most likely timing out at the default of 45 minutes, and you're most likely relying on WMI Probes, which are failing, because your hosts are not correctly configured to respond to the WMI Probes. Once the Probes fail, the user-ip mappings are deleted. Once they are deleted, Captive Portal will trigger. If the Captive Portal is set to its default Expiration of 60 minutes, then users will have to validate to CP every hour. By default, User-ID Cache timeout is set to 45 minutes. If users would be on site for a maximum of 12 hours, you can set the timeout to 720 minutes, and disable Probing. Note I'm making a lot of assumptions based on similar cases I've worked. Your settings may differ, in that case, I recommend you open a Support ticket and we can take a closer look. I also recommend checking out these documents: Best Practices for Securing User-ID Deployments User-ID Best Practices - PAN-OS 5.0, 6.0
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