Can't access wp.admin after 4.2.3 update!

I have a WordPress Multisite with 4 sites.
One of this is very big and has about 80k posts.

This night i updated to 4.2.3 and i get a Timeout Error.
So i raised the php_execution_time and the Apache and nginx Timeout and retry the update.

The update gone well and after this it ask me to update the entire network (is a Multisite WordPress).

It started but something gone wrong and i take a blank page.

I saw from PhpMyAdmin that not all the tables are converted to utf8mb4_unicode_ci. And also Frontend and Backend show blank page.

So i called https://site/wp-admin/update.php and https://site/wp-admin/upgrade.php and it started again a process where it tried to convert the charset of the tables but it stopped again.

At the moment not the entire db is converted to new charset and we have frontend working fine and backend with the error:

you do not have sufficient permissions to access this page

Any suggestion? I prefer avoid downgrade to 4.2.2 with previuos backup.