DMVPN don't work after upgrading a 1941 to a ISR4321

[CHRISTIAN BRAUN]

We want to remove our 1841/1941 DMVPN client Router's with new ISR4321.
On our Testlocation we replace a 1941 and move the config to the new Router.

Now we have the strange behavior that ISAKMP comes up (and is stable) but Phase 2 work only for round a about 5 sec then 1 min Phase 2 is down and then it works again for 5 sec.
During the 5 sec i can ping the central tunnel IP and IPSec (sh crypto ipsec sa) is in status ACTIVE
We have try different IOS (03.16.03.S and 03.13.04.S).
Config is exactly the same as on all other.

Any idea, what kind of problem we have?

[CHRISTIAN BRAUN]

We fix that problem accidently by upgrading to 16.2 and downgrading back to 15.x..

In 16.2 "ip nhrp registration no-unique" is default and disappear from running config ... and that fix the problem ... i'm very very annoyed