I started with Synergy in June 2016 and had the problem with Copy and Paste from the beginning. I used first 1.5.0, then v1.7.6, v1.8.8 and now v1.9.1.
Because I also use some machines with Debian and Ubuntu, I have never installed Synergy 2.
But one thing I noticed. I can leave the systems running for several days and copy and paste text hundreds of times, between different Synergy Clients, without any problem, as long as I do not copy on the same Linux system, between two Application, or two Terminal sessions.
Why I have not yet informed the support? Once stop and a few second