STILL having the issue. I have to restart lightroom about four times throughout a heavy working day, it starts to lag after I've gone through a few hundred images and optimization does not help. It's like the program is a funnel slowly filling up until I can't switch modules quickly anymore. Eventually every module switch or maximizing/windowing the interface takes seconds and I have to shut down lightroom. It's decent when I get it back up again but this is almost as bad as when it was crashing regularly on LR 5.4.
This is more than irritating, it's hurting my workflow considerably.