Critical error when setting new user password

Hi,

Over the past few weeks new users get an error message when their registration email is sent and they click on the link to create their password. The page loads, the user enters their password, and when they click Reset Password, it returns the following:

There has been a critical error on your website.
Learn more about debugging in WordPress.

Here’s what the log shows:

[03-Dec-2019 02:44:20 UTC] PHP Fatal error: Uncaught Error: Call to a member function exists() on null in /wordpress/core/5.3/wp-includes/user.php:1365
Stack trace:
#0 /wordpress/core/5.3/wp-includes/pluggable.php(2532): clean_user_cache(NULL)
#1 /wordpress/core/5.3/wp-includes/user.php(2453): wp_set_password('ChangeMe12345', NULL)
#2 /srv/htdocs/wp-content/plugins/uncanny-learndash-toolkit/src/classes/frontend-login-plus.php(1806): reset_password(Object(WP_Error), 'ChangeMe12345')
#3 /wordpress/core/5.3/wp-includes/class-wp-hook.php(288): uncanny_learndash_toolkit\FrontendLoginPlus::validate_reset_password('')
#4 /wordpress/core/5.3/wp-includes/class-wp-hook.php(312): WP_Hook->apply_filters(NULL, Array)
#5 /wordpress/core/5.3/wp-includes/plugin.php(478): WP_Hook->do_action(Array)
#6 /wordpress/core/5.3/wp-settings.php(523): do_action('init')
#7 /srv/htdocs/wp-config.php(84): require_once('/wordpress/core...')
#8 /wordpress/core/5.3/wp-load.php(42): require_once('/srv/htdocs/wp-...')
#9 /wordpress/core/5.3/wp-blog-header.php(13): require_once('/wordpress/core...')
#10 /wordpress/core/5.3/index.php(17): require('/wordpress/core...')
#11 {main}
thrown in /wordpress/core/5.3/wp-includes/user.php on line 1365

It doesn’t look like there’s any caching on that page. I’ve tried disabling all other plugins and it still won’t work.

We’re using the WP 5.3 and the latest version of Uncanny.

Help?