Hey @Scott,
I’m really sorry to hear about this βΒ to be clear, do you mean the “Attendees” link specifically that I highlight in the following screenshot?

If so, then when I click this link I am brought to the Attendees list admin view without issue.
To get started, can you share the “System information” for one of your sites? Here’s how to share system information with us β https://theeventscalendar.com/knowledgebase/sharing-sys-info/
You mention having ten sites with both plugins, but just for the sake of efficiency can you choose one website to focus on for now? We will focus on getting things working there then turn to each other website afterwards and apply the fixes. If issues persist on those other sites, we can handle those in turn from there.
Thank you!
George