On a multisite network dashboard with ACF Pro 5.2.3 there is a new database upgrade screen like so: https://cloudup.com/cG-CSsyYMoT. This screen get’s stuck when there are sites on the network which don’t have the ACF Pro plugin active. ACF Pro is not network activated on my install. See the issue with a workaround of activating the plugin here: https://cloudup.com/c63LcrgzZXG.
This issue appears to have gone away with ACF Pro 5.2.4.