I had been using samlauth module, and I wrote another module using tokens on hook_user_login.
The combination caused a problem because I didn't add a BubbleableMetadata object to the end of the \Drupal::token->replace() method.
The error was:
LogicException: The controller result claims to be providing relevant cache metadata, but leaked metadata was detected. Please ensure you are not rendering content too early. Returned object class: Drupal\Core\Routing\TrustedRedirectResponse. in Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext() (line 154 of /var/www/docroot/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php
$bubbleable_metadata = new BubbleableMetadata(); $output = $token_service->replace($config->get('format'), ['event-log' => $row], , $bubbleable_metadata);
Just thought this should exist somewhere to anyone else with this issue.