[Site Categories] Site Categories has stopped working

We have a problem with the “Site categories” plugin on our multisite. We migrated servers and updated to WP 5.0 and discovered that Site Categories had stopped working. The category page correctly displayed the categories, and with the correct counts. Trying to view the sub-pages produces a 404.

I contacted you via chat and we eliminated permalinks and the htaccess file as sources of the problem. You then suggested that all that was required was a slight nudge to set things right again. This sounded right. You also suggested that I ought to deactivate all of the plugins and then reactivate them one by one (the assumption being that Site Categories would start working when it was the only active plugin).

Not wishing to disrupt our site, we created a clone of the site to test upon – thus effecting a nudge of sorts (clone27….). The cloned site also exhibited the problem. I then deactivated all of the plugins with the exception of Beaver Builder and Wordfence. Site Categories still didn’t work.

We need your help to take this investigation further.

When does the plugin physically create the category sub-pages? Is it part of the “Add new site category” process? (I have successfully added new categories as part of my investigation). Is it possible that the pages are successfully being created, but that we are somehow losing the parent node?