I'm trying to hook up my two sons to 1Password and neither of them is able to connect to their vaults, despite all other connections working.
I've seen an earlier post on this topic written off as "security software in the way", but I've disabled Little Snitch (which is my only firewall software) and it didn't help.
When I look in the Console, I can see an error message (which summarised says):
OPAESKey: ... E decrypt: Decryption failed: ... Code = 506 "Decryption failed, bad HMAC"
(which is the message also shown here: https://discussions.agilebits.com/discussion/79965/1p-fails-to-unlock-and-errors-with-a-decrypt-bad-hmac-failure)
Your servers must be ok because they were able to connect their iPhones, the problem is on their 10.11.3 (El Capitan) MacBooks.
1Password Version: Not Provided
Extension Version: Not Provided
OS Version: 10.11.3
Sync Type: Not Provided