[Arm-dev] Weird issue with NFSv4

Hi there.

Strange issue with NFSv4 this morning.
RPI3b+ with kernel 103 and fresh yum update, set up as NFSv4 client.

Trying to copy a whole folder with a few GB (many .rpm & .tgz and a few 
.img), from NFS mounted source to local filesystem.
     (cd /shared.nfs ; tar c) | (cd /local ; tar x)

After a while ...
- PING to the RPI works.
- SSH sessions got frozen and login is impossible, even with USB 
keyboard on the RPI.
- Sometimes, I do see some kernel backtrace on the VGA, but not always.
As I have to switch off the RPI, there is nothing left in 
/var/log/message when system is back.

If I do this copy with full SSH, the copy works perfectly well.
     (ssh xxx "cd /xxx ; tar c") | (cd /local ; tar x)

I have the feeling that the system hangs often on the same huge file, 
but when I do copy it manually, even in a loop ... nothin happens.

Any idea ?