Thank you for the detailed description and the error logs, it helped me a lot.
The problem was an unsupported function call, which was introduced in plugin version 4. It seems like that in rare cases some wordpress installs does not have this enabled. I've made a tiny modification on the search code, it should work now.
This code part is going to be replaced in the upcoming version, so you don't have to worry about it anymore.Best,
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