After upgrade to nfs-utils-2.4.1, my clients were unable to mount nfs v3 exports with the following error in server logs:
rpc.mountd: can't stat exported dir /shared/folder: Invalid argument
Downgrading to nfs-utils-2.3.3 and everything works as expected.
Related bug on https://bugs.gentoo.org/688644 contains proposed patch for support/misc/xstat.c
This is not a kernel problem but a userspace problem.
Please report to the nfs-utils maintaner and/or on the firstname.lastname@example.org.