The most common cause is that your Smart License registration token was not flagged to allow export controlled features. As a result, any devices using the license registered using that token will be restricted from using strong crypto. You can re-register with a new license token and make sure to click the check box to enable export-controlled features when doing so.
This is equivalent to a traditional ASA not having the 3DES-AES activation key. ASAv and ASA on Firepower hardware use Smart license instead.
