Are you sure you are mapped to root?
What does ‘agentinfo YOURSERVER’ return ?
Ahh... the users file is blank. So easy I overlooked it. Thanks!
I have observed same issue. In my case it did not help me adding user mapping in users or users.local.
I checked user permissions in /etc/passwd
This user (root) is mapped in exports, changing passwd with - root:x:0:0:root:/root:/sbin/bash worked for me or one can map right user in exports file instead for root which has root privileges and bash permission in passwd.
nexec needs a valid shell... /sbin/nologin is not a valid shell...