The internal application protocol changed incompatibly.  Sorry, this is part of living on trunk.  It would be ideal if we could support rolling updates during development, but particularly at this stage, imposing that constraint would slow down innovation, wouldn't be 100% reliable, and wouldn't always be practical in any case.

This is almost certainly happening because we have enabled non-blocking i/o but not yet taken all the necessary precautions to detect and retry when reads/writes do not succeed.  I expect to work on this soon.  In the meantime, I suggest commenting out one line in ClusterSearcher.pm (only needed on the client node):

   +++ b/perl/lib/LucyX/Remote/ClusterSearcher.pm    @@ -53,7 +53,7 @@ sub new {             my $sock = IO::Socket::INET->new(                 PeerAddr => $shard,                 Proto    => 'tcp',    -            Blocking => 0,    +            #Blocking => 0,             );

I'll let you know when I think it's safe to make the i/o non-blocking once
again.