I've logged in via FTP and debugged through the process. I have found the cause and implemented a possible fix as well.
The issue was that WordPress was reporting that the items on that page were “single items” while it was not correct. I've added a different method to check that, now the plugin should appear correctly.
I will investigate this further on my test servers, and maybe ask the wordpress devs why the is_singular() function wasn't working as expected.
A permanent fix will be added to the next release of course.Best,
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