If an account is disconnected, it's greyed out in your list of accounts.

Please proceed as follows to activate the disconnected account again: 

‘Accounts’ > ‘select disconnected account’ > ‘click on the dropdown besides the account name’ > ‘Disconnect this account’ > ‘OFF’

The account is now displayed as active again in your account list.

If you hid an account, it is no longer visible in the list of accounts. 

Please proceed as follows, to see the hidden account again: 

‘Settings’ > ‘select credentials’ > ‘select the hidden account’ > ‘Hide this account’ > ‘OFF’