The main reason you’ll see a 502 bad gateway error is due to an issue with the web host. Sometimes a query, script, or request will take too long and so it is canceled or killed by the server. A lot of hosts, especially shared hosts add what they call a “kill script.” Basically what this does is it will terminate a request after a certain period of time so that it doesn’t take a site down or impact other users.
Since Event Espresso has no control over whether your host has a kill script in place, your can try this troubleshooting method:
Try temporarily deactivating all other plugins on the site and try those links again. If no Bad Gateway error with all other plugins deactivate, you reactivate the other plugins one-by-one until the you see the error again.