Please post the full error for this issue.
I’m not really sure how to do that, but I can give you a link to the full error logs for those days:
Your log is full of database query errors.
They seem to be caused by this plugin: WP_User_Frontend
And those errors affect BP but are not caused by BP, afaik.
You should ask the creators of WP_User_Frontend about your errors.
The sending of emails does not seem to be related to this error – and is most likely also not a BP issue.
[09-Jun-2020 20:37:10 UTC] WordPress database error You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘WHERE id = 51’ at line 1 for query SELECT * FROM WHERE id = 51 made by require(‘wp-blog-header.php’), require_once(‘wp-load.php’), require_once(‘wp-config.php’), require_once(‘wp-settings.php’), do_action(‘plugins_loaded’), WP_Hook->do_action, WP_Hook->apply_filters, WP_User_Frontend->plugin_upgrades, current_user_can, wp_get_current_user, _wp_get_current_user, wp_set_current_user, do_action(‘set_current_user’), WP_Hook->do_action, WP_Hook->apply_filters, wplr97_->wplg67rg, wplr97_->wplkzu6r, wplt4j15::wplno56a, xprofile_set_field_data, xprofile_get_field, BP_XProfile_Field::get_instance, BP_XProfile_Field->__construct, BP_XProfile_Field->populate
Just reached out to the creators of WP_User_Frontend. Thanks for your help.