Upgrade from 12.1.2 to 13.1.1.4

You need to verify below things while upgrading from one version to another version.

1. Vendor support is there or not?
2. Always activate license before upgrading the device.
3. Verify your configuration on F5 ihealth portal.
4. Normally you will see issues with https monitor, irules etc..
5. If servers which are behind F5 are legacy ones, they may not support new ciphers.

Other than above points upgrade will be smooth process. All the best for your activity.