I have the latest module 8.x-2.0 installed with a Drupal 9.0.7 site in development. Everything was working fine. But when I logged in as a regular authenticated user for testing purposes and I get to the Agreement page, the whole site template is rendered twice. The top half of the page shows the "C-clamp" of the site header, navigation, and footer, but with a blank page body and some of the blocks missing too. The second half of the page shows the same template with the agreement page content inserted. Until the agreement is accepted, every page is rendered twice. After the user accepts the agreement, the bug goes away.
See attached screenshot (blurred to protect content) for a quick visual.
Update: I traced the start of the issue back to when I enabled the Site Alerts module. The two modules appear to be incompatible for some reason.
Needs review
2.0
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Sorry for the very late response.
I looked at the site_alert module and I think the only thing that may be causing the double render is that the module has a route it loads via JavaScript, /ajax/site_alert.
If the agreement is configured with Visibility to "Show on every page except the listed pages", then adding that path to the Visibility Pages configuration will prevent the Agreement from rendering when that path is requested.