Error with the Amazon S3 add-on

When I try to download a file from Amazon via the Amazon S3 add-on (which has previously been working fine), I now get the following error:

Fatal error: Uncaught Error: Class ‘WPDM_Stats’ not found in /var/www/html/wp-content/plugins/wpdm-amazon-s3/wpdm-amazon-s3.php:392 Stack trace: #0 /var/www/html/wp-includes/class-wp-hook.php(286): WPDM_AmazonS3->Download(Array) #1 /var/www/html/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(”, Array) #2 /var/www/html/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #3 /var/www/html/wp-content/plugins/download-manager/wpdm-start-download.php(12): do_action(‘wpdm_onstart_do…’, Array) #4 /var/www/html/wp-content/plugins/download-manager/libs/class.Apply.php(417): include(‘/var/www/html/w…’) #5 /var/www/html/wp-includes/class-wp-hook.php(286): WPDM\libs\Apply->triggerDownload(”) #6 /var/www/html/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(NULL, Array) #7 /var/www/html/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #8 /var/www/html/wp-settings.php(450): do_action(‘init’) #9 /var/www/html/wp-config.php(188): require_once(‘/var/www/html/w…’) #10 /var/www/html/wp-load.php(37): req in /var/www/html/wp-content/plugins/wpdm-amazon-s3/wpdm-amazon-s3.php on line 392

I’ve tried de-activating, then deleting, and then re-installing and activating the Amazon S3 add-on, but the same error keeps coming up.

Other strange things I’ve noticed:

a) In Downloads ► Add-Ons, I don’t see a list of add-ons.
https://www.screencast.com/t/7M2LarZE5YO

b) In Downloads ► Settings ► Updates, I no longer see my purchased add-ons, even though it’s installed and activated.
https://www.screencast.com/t/xuNTjj9QS
https://www.screencast.com/t/F1mp4kyBOpA

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WPDM – Amazon S3 version: 2.6.4

I decided to try upgrading to WP Download Manager Pro (rather than using the free edition), in the hopes that it would resolve the current bug I was seeing with the Amazon S3 paid add-on.
Doing this appears to have resolved the issue.
So the bug must be limited to the free edition of WP Download Manager.