Links work fine but not tooltips

I’m a total newbie with WP.
My browser views the hover-over tooltips on other sites perfectly, but on my own site the links work fine, but the tooltip displays “This reference could not be loaded at this time”. I’ve tried Chrome, Edge, Safari (iOS). All the same; they work fine if I visit reftagger.com and try their sample.
I’m guessing it’s something about how I’ve set up WP.
Help please…

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