I installed the code, signed into the Dashboard, then opened the Members page on the front end. This is what debug.log contains:
2023-09-20 13:34:52 user_id 0 WP error code empty_username, message <strong>Error:</strong> The username field is empty., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: user.php:148, WP: class-wp-hook.php:310, WP: plugin.php:205, WP: pluggable.php:618, WP: user.php:106
2023-09-20 13:34:52 user_id 0 WP error code empty_password, message <strong>Error:</strong> The password field is empty., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: user.php:152, WP: class-wp-hook.php:310, WP: plugin.php:205, WP: pluggable.php:618, WP: user.php:106
2023-09-20 13:34:58 user_id 0 WP error code invalid_username, message <strong>Error:</strong> The username <strong>[email protected]</strong> is not registered on this site. If you are unsure of your username, try your email address instead., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: user.php:166, WP: class-wp-hook.php:310, WP: plugin.php:205, WP: pluggable.php:618, WP: user.php:106
2023-09-20 13:34:58 user_id 0 redirect by WordPress, 302, https://milltownquilters.com/wp-admin/ stack trace: WP: class-wp-hook.php:310, WP: plugin.php:205, WP: pluggable.php:1433
2023-09-20 13:35:00 user_id 1054 WP error code invalid_taxonomy, message Invalid taxonomy., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: taxonomy.php:1299, wp-slimstat/admin/view/wp-slimstat-reports.php:1739, wp-slimstat/admin/view/right-now.php:193, wp-slimstat/admin/view/wp-slimstat-reports.php:1196, wp-slimstat/admin/view/wp-slimstat-reports.php:959
2023-09-20 13:35:00 user_id 1054 WP error code invalid_term, message Empty Term., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: taxonomy.php:4593, wp-slimstat/admin/view/wp-slimstat-reports.php:1741, wp-slimstat/admin/view/right-now.php:193, wp-slimstat/admin/view/wp-slimstat-reports.php:1196, wp-slimstat/admin/view/wp-slimstat-reports.php:959
2023-09-20 13:35:00 user_id 1054 WP error code invalid_term, message Empty Term., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: taxonomy.php:4593, wp-slimstat/admin/view/wp-slimstat-reports.php:1741, wp-slimstat/admin/view/right-now.php:193, wp-slimstat/admin/view/wp-slimstat-reports.php:1196, wp-slimstat/admin/view/wp-slimstat-reports.php:959
2023-09-20 13:35:00 user_id 1054 WP error code invalid_taxonomy, message Invalid taxonomy., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: taxonomy.php:1299, wp-slimstat/admin/view/wp-slimstat-reports.php:1739, wp-slimstat/admin/view/right-now.php:193, wp-slimstat/admin/view/wp-slimstat-reports.php:1196, wp-slimstat/admin/view/wp-slimstat-reports.php:959
2023-09-20 13:35:00 user_id 1054 WP error code invalid_term, message Empty Term., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: taxonomy.php:4593, wp-slimstat/admin/view/wp-slimstat-reports.php:1741, wp-slimstat/admin/view/right-now.php:193, wp-slimstat/admin/view/wp-slimstat-reports.php:1196, wp-slimstat/admin/view/wp-slimstat-reports.php:959
2023-09-20 13:35:00 user_id 1054 WP error code invalid_term, message Empty Term., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: taxonomy.php:4593, wp-slimstat/admin/view/wp-slimstat-reports.php:1741, wp-slimstat/admin/view/right-now.php:193, wp-slimstat/admin/view/wp-slimstat-reports.php:1196, wp-slimstat/admin/view/wp-slimstat-reports.php:959
2023-09-20 13:35:00 user_id 1054 WP error code invalid_taxonomy, message Invalid taxonomy., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: taxonomy.php:1299, wp-slimstat/admin/view/wp-slimstat-reports.php:1739, wp-slimstat/admin/view/right-now.php:193, wp-slimstat/admin/view/wp-slimstat-reports.php:1196, wp-slimstat/admin/view/wp-slimstat-reports.php:959
2023-09-20 13:35:00 user_id 1054 WP error code invalid_term, message Empty Term., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: taxonomy.php:4593, wp-slimstat/admin/view/wp-slimstat-reports.php:1741, wp-slimstat/admin/view/right-now.php:193, wp-slimstat/admin/view/wp-slimstat-reports.php:1196, wp-slimstat/admin/view/wp-slimstat-reports.php:959
2023-09-20 13:35:00 user_id 1054 WP error code invalid_term, message Empty Term., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: taxonomy.php:4593, wp-slimstat/admin/view/wp-slimstat-reports.php:1741, wp-slimstat/admin/view/right-now.php:193, wp-slimstat/admin/view/wp-slimstat-reports.php:1196, wp-slimstat/admin/view/wp-slimstat-reports.php:959
2023-09-20 13:35:00 user_id 1054 WP error code invalid_taxonomy, message Invalid taxonomy., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: taxonomy.php:1299, wp-slimstat/admin/view/wp-slimstat-reports.php:1739, wp-slimstat/admin/view/right-now.php:193, wp-slimstat/admin/view/wp-slimstat-reports.php:1196, wp-slimstat/admin/view/wp-slimstat-reports.php:959
2023-09-20 13:35:00 user_id 1054 WP error code invalid_term, message Empty Term., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: taxonomy.php:4593, wp-slimstat/admin/view/wp-slimstat-reports.php:1741, wp-slimstat/admin/view/right-now.php:193, wp-slimstat/admin/view/wp-slimstat-reports.php:1196, wp-slimstat/admin/view/wp-slimstat-reports.php:959
2023-09-20 13:35:00 user_id 1054 WP error code invalid_term, message Empty Term., data stack trace: WP: class-wp-hook.php:312, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: class-wp-error.php:209, WP: class-wp-error.php:66, WP: taxonomy.php:4593, wp-slimstat/admin/view/wp-slimstat-reports.php:1741, wp-slimstat/admin/view/right-now.php:193, wp-slimstat/admin/view/wp-slimstat-reports.php:1196, wp-slimstat/admin/view/wp-slimstat-reports.php:959
2023-09-20 13:35:19 user_id 1054 redirect by WordPress, 301, https://milltownquilters.com/members/ stack trace: WP: class-wp-hook.php:310, WP: plugin.php:205, WP: pluggable.php:1433, WP: canonical.php:805, WP: class-wp-hook.php:310, WP: class-wp-hook.php:334, WP: plugin.php:517, WP: template-loader.php:13
I also ran it on my local machine for comparison and the only difference was that on the local machine, none of the WP error code lines had any information in the stack trace section.
Since slimstat seems to be coming up a lot, I tried deactivating it again in case I had missed it before, but the Members page still comes up empty.