TYPO3 Core

Configure a rootpage uid 1.

Add a siteconfiguration for it.

Enable ext:workspaces

create a workspace

switch to the created workspace

edit/go-to the page-properties of the rootpage uid 1.

change some page-property values

save and close. cough I mean: close and click save in the dialog-modal.

once again edit page-properties of the rootpage uid 1.

WHOOOOOPS - looks like something went wrong!

No site found in root line of page 2

in /var/www/html/private/typo3/sysext/core/Classes/Site/SiteFinder.php line 138
            if (isset($this->mappingRootPageIdToIdentifier[(int)$pageInRootLine['uid']])) {
                return $this->sites[$this->mappingRootPageIdToIdentifier[(int)$pageInRootLine['uid']]];
            }
        }
        throw new SiteNotFoundException('No site found in root line of page ' . $pageId, 1521716622);
    }

    /**
     * @param bool $useCache

This is happening in TYPO3 v9. I guess this is still the case in v10 too.