[Proven]

You could have moved to another native AWS service that works (FSx for NetApp).

FSxN (https://aws.amazon.com/fsx/netapp-ontap/)

As others have mentioned among non-native services (not sure if that's acceptable to you, but it is to some) there are many 3rd party solutions that work better with NFSv4.

[dallbee]

Our product supports what our customers use, which in this case was EFS. Doesn't really matter if there's better implementations available.