I’ve been locked out from my drives today now too since the firmware update.
27" 2013 iMac
OSX 10.11 (El Capitan)
I can log into the web admin just fine. View and access files from there, but now there is no way to connect to the drives in the system browers. Tells me unable to connect. Same IP addresses. The drive is recognized and shows up fine everywhere else. Even the My Cloud EX4 software sees the drive but is unable to access to make the file browser connection.