Uncaught TypeError: Cannot read property ‘results’ of null

I get the following error when I attempt to begin the tagging process:

Uncaught TypeError: Cannot read property 'results' of null
    at Object.success (tmt-admin.js:56)
    at i (load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-position,utils,suggest,jquery-ui-menu,wp-a11y,jquery-ui-aut&load[]=ocomplete,tags-suggest,underscore,moxiejs,plupload&ver=4.9.4:2)
    at Object.fireWith [as resolveWith] (load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-position,utils,suggest,jquery-ui-menu,wp-a11y,jquery-ui-aut&load[]=ocomplete,tags-suggest,underscore,moxiejs,plupload&ver=4.9.4:2)
    at y (load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-position,utils,suggest,jquery-ui-menu,wp-a11y,jquery-ui-aut&load[]=ocomplete,tags-suggest,underscore,moxiejs,plupload&ver=4.9.4:4)
    at XMLHttpRequest.c (load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-position,utils,suggest,jquery-ui-menu,wp-a11y,jquery-ui-aut&load[]=ocomplete,tags-suggest,underscore,moxiejs,plupload&ver=4.9.4:4)

Selecting “My website is not publicly accessible” works until I get:

Uncaught TypeError: Cannot read property 'map' of undefined
    at Object.success (tmt-admin.js:56)
    at i (load-scripts.php:2)
    at Object.fireWith [as resolveWith] (load-scripts.php:2)
    at y (load-scripts.php:4)
    at XMLHttpRequest.c (load-scripts.php:4)

Tagging is now stuck after 83 images.

WordPress 4.9.4 | PHP 7.1.15 | Apache/2.4.29 (Unix) mod_hive/6.6 OpenSSL/1.0.1e-fips mod_fastcgi/2.4.6 | MySQL 5.6.36-82.1-log

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