Sometimes in the last month or two Inkscape developed a crippling lag. "Lag" is not even the right word. All the windows lose focus in the middle of doing something. Merely dragging a selection rectangle is an exercise in frustration, and it is actually impossible to rename a layer (because the typing box is dropped before you can get more than two characters in).
I'm frustrated enough to give up on it now, despite it having been a mainstay of my graphic/2D CAD work for years now. I just wasted an entire potentially productive day trying to get it to work again, and that is on top of several days and multiple hours of previous attempts.
Here's what I've tried:
Hunting through Preferences and turning down all the various aliasing and so forth (things that are described as causing "slow" behavior)
Trying on clean and new files.
Playing with the X11 settings.
Reverting to an older version of Inkscape.
Deleting the preferences and the Apple applications state files.
Reverting to an older version of Xquartz.
Checking endless forums for help.
Trying (and failing) to register at the official forums to get help.
Trying (and failing) to get into the bug reporter.
Nothing has had a measurable effect on the problem. I can't even draw a rectangle without the selection dropping in the middle.