NFS root permission denied in 'clearcritlocal'?

I've maintained netboot/NFS-root setups for my machines for well over
a decade, but recently something broke and now when '/etc/rc' runs on
a diskless client, the cleanup of "/var/run/" in '/etc/rc.d/clearcritlocal'
fails with all 'rm' attempts claiming "permission denied".

NFS root directories (which include "/var") are exported only to
each individual host with "-maproot=root" and shared directories
("/usr", "/var/lib") are exported to a netgroup of same-arch hosts
also with "-maproot=root".

So far, I've seen this only on a BeagleBoneGreen (evbarm-earmv7hf)
with 11.0_RC3 and an amd64 client booting 11.99.5.

i386/11.99.5 and sparc/11.0_RC3 still seem to work properly, although
I should check again.

The file server was running 11.0_RC3, now updated to the latest 11.0_RC4.

To facilitate a 'qemu-system-sparc' guest to mount my pkgsrc tree via
NFS, I had to modify the export to the host system (amd64/10.1_STABLE)
to include "-noresvport -noresvmount".

I did notice a message from 'mountd' the last time I rebooted the file
server about "Can't update exports for <exported fs> (Operation not
permitted)", but I haven't investigated it yet.

Perhaps it doesn't like conflicting flags and/or host/network
configuration.  Later, during the attempt to netboot the amd64 client
with 11.99.5 a mountd process claimed "Can't send reply".

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