So I started testing 2.6.0 (running on bamboo build 207) with fastpath and have some bug fodder for you
1) In Spark 2.5.8, if I was a member of more than one workgroup, after exitting and restarting spark client, i'd be logged in to whichever group I was last logged in to. In 2.6.0 I start logged out.
2) Using the webchat plugin, I get entered to a queue, the agent accepts, gets a chat window, but when the queue window switches to the chat window I immediately get a popup (in webchat) saying that it could not connect me to an agent (see screenshot.png) However, when I tried to type in the chat (from agent side) anyway, I was able to see it in the webchat after closing the JS popup momentarily before it switched me to the offline screen (I couldn't get a screenshot of that). In a second attempt, I did get a screenshot (screenshot1.png) of the agent console showing the user had disconnected, and the user console getting a message that the agent had closed the chat (none of that actually happened - I just kept the JS popup waiting a few minutes while I was working with the screenshots and writing this message) - the message appeared after closing the first JS popup. Also note in this screentshot that the agent name isn't being recieved by webchat properly. After a third long wait for that popup I got another odd one (screenshot2.png) after dismissing that one it forcefully closed the chat window.
3) Adding the (windows) builds to client-control plugin deploys them, but even after the upgraded version is installed, the client pops-up the upgrade window.
4) The client-control uploader is not working at all between nightly builds. For example, a client on my network running 204 gets the upgrade notice for 207, but the download never happens (screenshot3.png)