Thank you!
Okay, I think I see what the issue is. It is actually caused by the fact that the plugin tries to push the member results to the results page, but the results page fails when it tries to display that. It happens, because WordPress results pages are only meant to display post type results. In this case is seems to be very specific for projects. The plugin gets by this issue by creating a “fake” post type object and replacing the post fields with the appropriate user details, unfortunately there is no better way of doing it currently with WordPress.
My guess is, that the results page probably uses a custom loop/grid template or widget specifically made for only post types content, and during the processing of the results it may try to get a field value, which does not exist and it ends up in an error message.
You could theoretically experiment with changing the results page, but I don’t know if it’s worth it. You could either use only the live search feature – or try to use the results shortcode as a custom results page for that specific search bar. With that solution you can keep the results page as is, and use another singular page for the member results.