seeing PHP error with WPSuperCache in my httpd log

I was checking my server log (Apache 2.4 on Amazon Linux) and found an error related to WP Super Cache that keeps recurring:

PHP Fatal error: Uncaught Error: Call to undefined function set_transient() in /var/www/html/wp-content/plugins/wp-super-cache/wp-cache-phase2.php:1049\nStack trace:\n#0 /var/www/html/wp-content/plugins/wp-super-cache/wp-cache-phase2.php(1043): wp_cache_replace_line('^ *\\\\$wp_cache_d...', '$wp_cache_debug...', NULL)\n#1 /var/www/html/wp-content/plugins/wp-super-cache/wp-cache-phase2.php(926): wp_cache_setting('wp_cache_debug_...', '35913a65cd9504d...')\n#2 /var/www/html/wp-content/plugins/wp-super-cache/wp-cache-phase2.php(478): wpsc_create_debug_log('35913a65cd9504d...', '1bb439346a15a92...')\n#3 /var/www/html/wp-content/plugins/wp-super-cache/wp-cache-phase2.php(328): wp_cache_debug('wp_cache_get_co...', 5)\n#4 /var/www/html/wp-content/plugins/wp-super-cache/wp-cache-phase1.php(54): wp_cache_get_cookies_values()\n#5 /var/www/html/wp-content/advanced-cache.php(22): include_once('/var/www/html/w...')\n#6 /var/www/html/wp-settings.php(84): include('/var/www/html/w...')\n#7 /var/www/html/wp-config.php(91): require_once('/var/www/html/w. in /var/www/html/wp-content/plugins/wp-super-cache/wp-cache-phase2.php on line 1049

What is exactly is my server trying to tell me about WPSuperCache and how can I fix it?

Using version 1.6.1 of the plugin with WordPress v. 4.9.6.

Thank you.