About 1/2 an hour ago the game was lagging so bad it was unplayable. Cleared cache did nothing. Reloading game and browser did nothing. Checked memory usage. 8 gig maxed out. Hmmm. Shut down browser and reopened it and cleared cache. Memory still maxed out. Rebooted PC; problem currently fixed.
Had a nosy on line and found some interesting notes. Seems that this update "Windows 10 v1709 " has created some memory leak issues.