Not a fix but it's a workaround to keep from crashing when working on plots.
There's a folder named "structures" on your hard drive. This is where the models are kept. The crashing is caused by the rotating model in the construction view tab of the plot window (found by testing last night, crashed over 50 times in 2 hours running tests).
Renaming that folder before starting horizons will prevent any structures from being viewable in the game (just the pointer placeholder). That's the bad thing. The great thing is that the models will also not display in the construction window and it will not crash you.
It may be that you can rename the folder after logging in so you get the buildings in the game but not the models in the construction window (2 hours last night, too tired to run any more tests).
My guildmates saw me popping in and out and were trying to get me to stop, until they found out I knew a workaround to the crashing[:P]