I tried adding a "travel" tag to my passport in the Passport category on both my iPhone 6S and iPad 4 mini. In both cases the whole app crashed and the dialogue box for sending a crash report popped up the next time I launched 1P. I continued to troubleshoot and I am successfully able to add tags to login, credit cards & secure notes categories so right now it's specific to the Passports category.
Easily reproducible on both devices.
1Password Version: 6.4 (640007)
Extension Version: Not Provided
OS Version: 10.11.4
Sync Type: Famililes