Plugin: Organize Series, Pages will not load "catchable fatal error"

The links listed below will not load, instead the following error message is provided:
Catchable fatal error: Object of class WP_Error could not be converted to string in /home/…/wp-content/plugins/organize-series/orgSeries-template-tags.php on line 876

https://loveanyway.theherosspouse.com/book-review/book-review-runaway-husbandsthe-abandoned-wife%E2%80%99s-guide-to-recovery-and-renewal/
https://loveanyway.theherosspouse.com/book-review/book-review-runaway-husbandsthe-abandoned-wife%E2%80%99s-guide-to-recovery-and-renewalpart-ii/
https://loveanyway.theherosspouse.com/book-review/book-review-runaway-husbandsthe-abandoned-wife%E2%80%99s-guide-to-recovery-and-renewalpart-iii/
https://loveanyway.theherosspouse.com/book-review/book-review-runaway-husbandsthe-abandoned-wife%E2%80%99s-guide-to-recovery-and-renewalpart-iv/

I don’t know if this issue is about the series plugin, but the string referenced in the error message referenced the plugin. But other series load without a problem.
I tried to see if I could edit the url of the page and I could not. I did have the ability to edit other posts that were from around the same time period and part of series.
Since these posts are from 2011 I had not tried to access them and thus do not know how long they have been inaccessible; a reader notified me about the problem.

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