I have found the problem with related posts pro and that plugin. RPP recognized each post as an individual single post and executed itself, so it took too much resources. (the internal is_single() wordpress call returned true) I guess it's because the toolset plugin uses WP_Query and it acts as if all the present items are single ones.
Anyways, I've added an exception to not execute the plugin in that case. It appears to be working now.
I checked the performance tracker, and the search queries appear to be all right in, they are executed under 0.1 seconds, so the database can keep up with that.
I'm going to fix that for the next update of course, until then you can safely use it without the cache. Sorry about that inconvenience.Best,
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