By default at least on Centos 7 nfs only allows 8 connections and starts 8 nfsd daemons.
To fix this edit this file: /etc/sysconfig/nfs
Edit the line "RPCNFSDCOUNT" (uncomment it so it looks like this:
RPCNFSDCOUNT=30
In the example above we are setting 30 nfsd daemons to run (or in other words 30 connections are possible this way).
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