The statements that created the points are exactly the same in the plugin as was used to create the points in the Ruby Console.

   pts=[]
pts.push Geom::Point3d.new(1,1,1)
pts.push Geom::Point3d.new(2,2,2)
pts.push Geom::Point3d.new(1,1,1)
pts.push Geom::Point3d.new(3,3,3)
pts.push Geom::Point3d.new(2,2,2)
pts.push Geom::Point3d.new(1,1,1)
   pts.uniq!

In the plugin nothing is removed as pts.length is 6 before and after the uniq! statement.
In the Ruby Console the 3 duplicates are removed.

In the Ruby console, if I create a series of 3d points and save them in an pts array then enter pts.uniq!, the duplicates are removed. But if I do the same thing in a plugin and execute the plugin nothing is removed. There is no indication of an error.

Dan, It turned out to be an unneeded View.invalidate statement.
Once it was removed, all was OK.

I don't have any UI.start_timer blocks so that can't be the problem. I did copy the entire code statement "UI.messagebox("There are no valid snap points", MB_OK)" to the console and the message displayed normally. I even added a UI.inputbox statement to see if it would display and, like messagebox, the tone sounded but nothing displayed. Other than a method that does a calculation, I can't think of anything in this plugin that I have used many times before.

In the middle of testing out a new plugin I was creating, the UI.messagebox stopped displaying. The command was being executed because I could hear the beep and the plugin would lock up until I pressed Enter. I added a UI.messagebox command in a reset method that is executed when plugin starts and that one displayed as expected but no other messageboxes after that.