Jive Cloud release 3006.x introduced a change in token authentication mechanism that sets the maximum token validity to 48 hours. That means any user with no activity on the Jive Community will be automatically logged out after 48 hours.
However, you notice that even the users who are actively using the Jive Community such as in the middle of browsing the spaces/content, reading through blog posts, or making any changes to the content are forcefully being logged out and have to log in again. In some cases with SSO configurations (authentication time > 48 hours at the SSO service provider's end), refreshing the browser window will log the users back in as well.
This issue was identified as a bug and resolved in Jive Cloud release 3006.8 with the issue key JVCLD-115548 (release notes on Worx). While the Cloud upgrades are automatically deployed, if you haven't yet been upgraded or have chosen to stay on an earlier version and now would like to upgrade, please get in touch with your Account Manager/Executive to arrange for the upgrade.
Any users actively using the Jive community shouldn't be logged out automatically after the upgrade.