What steps will reproduce the problem?
1. Use your own keystore file (store.bks) for a self signed certificate
2. Set the password for the keystore and try to connect to your ttrss server
3. Watch the error of keystore file cannot be opened with debugging

The bug seems to be in Controller.java, the password for the keystore is never 
read from preferences and thus is unset.

Comments in line 262 (method getKeystorePassword()) state: 
// Initialized inside initializeController();
but I cannot find any initialization there. 

After adding the following in getKeystorePassword():
if( keystorePassword == null) 
  keystorePassword = prefs.getString(Constants.KEYSTORE_PASSWORD, Constants.EMPTY);
it works again as expected.