Multisite Language Switcher connection only works on one page

I created a multisite network with two pages. I installed the Multisite Language Switcher plugin and activated it on both pages (German and French). Unfortunately, the plugin (more precisely the connection between both pages) only works properly on the French page. On the German page (main page) the following message is shown in the metabox: “You should define at least another blog in a different language in order to have some benefit from this plugin!”

I have a super-admin user who is authorised on both pages. I also deleted and re-installed the plugin but it didn’t make any difference. What could be the problem here?

Thank you!