I am having a similar issue however my backend locks up only when I try to change the (brand new, blank) products' attribute set.
I have noticed that when changing the attribute set, that the price field is highlighted red with "This is a required field" behind the loading overlay. Perhaps there is something internal going on that is preventing the page to load/switch because the required field is not letting the page move. I think of this similar to when you're on another website and you are prompted with "Are you sure you want to leave this page? There are unsaved changes." or something along those lines.
I will post back if I can find a cause or an answer! You should do the same. 
System: Magento 2.1.2 on Ubuntu 16.04 w/ Apache2.4, PHP 7.08, and MySQL 5.7.
PS I have a funny feeling too that it could be a PHP memory_limit problem, however I have my CLI and webserver php.ini memory_limits set to 768M which is the recommended memory_limit for Magento 2.
Update:
So I opened up the console log on the product page and clicked a new attribute set from the list. I then recieved this error and a stack trace.
Haven't found out what exactly the issue is, but it is stemming from `<magento_install_dir>/pub/static` and not from anywhere else; At least for my instance of the bug we've ran into that is.
From here I am wondering if a `$ magento setup:static-content:deploy` and/or a `$magento setup:di:compile` would resolve the issue. Will report back.
