I ran the Hummingbird Pro update just now & it has taken out my entire multisite!
White screens all around the WordPress Dashboard! And also the layout of the subsites those are using Upfront is broken.
There is the following error in debug.log
[15-Mar-2018 09:42:25 UTC] PHP Fatal error: Uncaught exception 'Exception' with message 'DateTime::__construct(): Failed to parse time string (1970-01-01 Array:00) at position 11 (A): The timezone could not be found in the database' in ***/wp-content/plugins/wp-hummingbird/core/pro/modules/class-module-reporting-cron.php:246