Okay, so this is a bit of a weird one, and I couldn't find anything else in the forum about it, so here goes. I'm on a System76 laptop with Ubuntu 15.04, running Diablo 3 via CrossOver 14.1.0 on a processor/graphics card that can far beyond handle it. In fact, when playing single player, the game runs quite smoothly in windowed mode, and only has a few weird cursor issues in fullscreen/windowed fullscreen that I think others have pointed out (separate post about that shortly).
However, after playing for a short time in multiplayer, e.g. a 2-player game shortly after completing a rift (lesser or Greater), my keyboard input begins to only accept new input at steady intervals. It could be for 1 second every 6, or for .2 seconds every 10, but for the remainder of the time, the keyboard is functionally nonexistent. The interval changes upon new iterations of the issue, i.e. restarting Diablo 3 and rejoining a multiplayer game. Things I've noticed so far:
1) It definitely only occurs in a multiplayer environment
2) It continues (single or multi) until restart
3) The farthest I can get without the issue occurring is by starting a single player, having someone join, and completing a rift together. Upon going back to town post-rift, problems occur. They are also always immediate if I join another's game.
4) The delay is varied per instance, ranging from a blip every few seconds to completely unresponsive keyboard
5) It only includes Diablo itself; all other keyboard input is still recognized by anything else, i.e. window manager, Mangler, etc.
I'm out of ideas for either what to test or what to try, so if anyone has any ideas on either side, please let me know; I'm happy to try anything that may help fix this issue.