NFS server messages "nfsd: peername failed (err 107)!", NFS clients freeze for a few minutes

Issue

• NFS clients keep freezing for a few minutes.
• NFS server /var/log/messages contains

Sep 20 04:38:03 myserver kernel: nfsd: peername failed (err 107)!  
Sep 20 04:45:38 myserver kernel: nfsd: peername failed (err 107)!  

or

Sep 20 04:50:10 myserver kernel: xs_tcp_setup_socket: connect returned unhandled error -107

• At the same time, an NFS client /var/log/messages may contain not responding, still trying

Sep 20 04:51:04 myclient kernel: nfs: server myserver not responding, still trying
Sep 20 04:51:04 myclient kernel: nfs: server myserver OK