El Capitan client ; Linux server - won't connect

[Graham Nicholls 0]

I can't seem to find if this is a known problem, but I have the latest versions (I believe - see below) minilinux:grahamn@~/src/tools/rrd $synergys --version synergys 1.7.4, protocol version 1.6 Copyright (C) 2012-2014 Synergy Si Ltd. Copyright (C) 2008-2014 Nick Bolton Copyright (C) 2002-2014 Chris Schoeneman minilinux:grahamn@~/src/tools/rrd $ And on the mac I've reinstalled 1.7.4 This is synergy pro, BTW - I've registered (twice - and paid twice). There is no firewall between the 2 machines. The server is running, and I can telnet to 24800 on the server from the client ( I get the string Synergy returned, helpfully). This worked before I upgraded to 10.11 on the mac. The debug window on the mac simply loops around NOTE: connecting to '192.168.50.2': 192.168.50.2:24800 WARNING: failed to connect to server: Timed out DEBUG: retry in 1 seconds. Both machines know each other by name and by IP. SSL is disabled. Accessibility config includes synergy on the mac. For years, synergy just worked. Now it's a PITA - even before the upgrade, I'd have to regularly restart both client and server. What has gone wrong?