I think I know why some images are missing. For example on page “James Tuvell” there is no image, but on page “Eben Joel” there is. The only difference is, that on “James Tuvell” page the featured image is missing. If you set the missing featured images, they should start appearing.
As for the performance, it's kind of fluctuating on my end, but the built performance tracker is reporting very low response times (around 0.08 – 0.1 seconds): https://i.imgur.com/8yrGhEK.png
This means that during the ajax request, ajax search pro only takes 0.08 seconds to finish. The rest of the execution time is the wordpress core loading, other plugins loading, theme loading etc..
Still, there are number of things you can do to improve the search performance, as described in chapter 18 and 18.1 in the documentation.
If the suggestions from chapter 18.1 does not make significant changes, I suggest trying to run a few tests with the P3 (plugin performance profiler) plugin to get a better insight on how the site loading time is distributed.
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