Why email took time to arrive or not working
Why email is not working
Please make sure if emails are not in spams or junks folders.
Why email took time to arrive
Email delay(arrival to the inbox) could be due to any reason. First of all, this could be your email content. Some email providers like Gmail take time to read content and decide to either put it to spam or in the inbox.
So your content should be strong and don't write such kind of content which could be suspicious.
This is not related to the theme because when any event trigger then it send an email because PHP functions run.
For testing purposes, you can install this plugin https://wordpress.org/plugins/email-log/
When your click it will trigger an email and you can see the email log it on the back-end.