The reason that this plot slows things down has to do with the large number of color scrollers. DMX devices are meant to be connected to a light that "owns" them. This happens dynamically through the ownerID field. When a light is added or deleted to a plot, LXBeams checks to see if it is owned or should be owned by any devices.
What was happening was that each of the color scrollers looked like they should be connected to an owner. LXBeams searched through all the plot's lights in an attempt to find the owner for each of the scrollers for each of the pasted lights. This ended up wasting a lot of time and temporary memory. The crash came because the application ran out of memory.
There were several ways to make the dynamic device/owner update more efficent. There will still be a small lag deleting and pasting a number of lights. LXBeams will still check all the devices for each new light. But it will be quicker about it and won't use up all the memory in the process.
It is inevitable, because of the way objects are dynamically linked, that a large number of lights and positions on the same layer will take a few seconds to update. It is great to have a plot with 400 plus lights in one layer to reveal where the slow points are. Thanks!