I would first like to know what steps you already took to try to fix the issue.
As the error message suggests, it probably is due to plugin conflict or customizations.
Have you tried testing for a plugin conflict? You can do this by deactivating all third party plugins, and seeing if the problem remains. If it's fixed, you'll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.
Below are additional general solutions you could try. Some of it might not be related to this issue but might prevent future errors:
Please check for the following first:
Ensure everything is up to date. Please check our Changelog.
Clear all caches including browser cache then deactivate your caching plugins and other optimization plugins.
If you're using a CDN, please clear the CDN's cache and disable optimization services.
Contact your host to increase your allocated memory or do it yourself by adding this code in your wp-config.php
define( 'WP_MEMORY_LIMIT', '256M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );