This is not a WPLMS issue the email is sent by buddypress plugin.
If the wp gmail smtp plugin is not working then try using some other third party email plugin like postman smtp plugin.
Please try using
postman smtp plugin : https://wordpress.org/plugins/postman-smtp/
Follow this guide for POSTMAN SMTP PLUGIN.
1. Install the Postman SMTP plugin from WP Admin - Plugins - Add New
2. Follow the setup wizard as below screenshots :
3. The outgoing Mail server should be :
smtp.gmail.com
4. Note the Port : 587
6. Enter you gmail USERname and Password.
7. Testing emails.
Please let me know if you need further details on this.