Why social networks can disconnect

Single Posts, Scheduled posts, Campaigns will not publish when a social networks are disconnected. Also analytics data will not be collected for social network.
What is the reason of the disconnection?
How to identify a disconnection and how to reconnect a social networks?

At the moment, there is one main reason – this is an authorization error. Such an error occurs when:
1) change the password in the social account;
2) changing the name of the social account (pages, groups, events, etc.);
3) when you remove WoofyApp from the Facebook group for Facebook