Windows won't close. Spark 2.6.3, Mac

Hello All.

I am new to the community.  I have been using Spark 2.6.3 on Mac OS X (10.9 Mavericks) for about 2 months. I've been having the same problem the entire time. When I open a Spark window to message a co-worker, I cannot close the window. When I click the red x to close the window, the contents of the window just go blank and the window sits there. If I want the window to go away, I have to quit Spark and re-launch it.

I searched the community and couldn't find anything about this, so if this is a known issue, please excuse my ignorance.

Please help, and thank you,

Jonathan