Can you please add a relevant URL where I can test the issue? Temporary FTP and back-end access would be very helpful too, in case the issue is in relation with the plugin. It will make the debuggin possible. Thank you!
I managed to find and correct the issue. Another plugin hook set one query variable (post__in) to a boolean “false” value, which triggered the error. I have added a line of code to the plugin to double check the query variable before use, it will be okay now.
I will make sure to include this change in the next patch, so you don’t have to worry about it anymore.