I am playing the latest test version (Beta_0.77b.278074) as the Mimot Brotherhood and have reached a point where performing a specific set of moves will crash the game.  The steps to recreate are:

1. Load the save located in DropBox at: https://www.dropbox.com/s/rvypp1hafmj8gp4/CrashDemo.GC4Sav?dl=0
2. Click your way through all of the "Contract Traders Complete" and "Research Mission Complete" windows (please see my previous post suggesting that you consolidate all of these windows into a single summary window).
3. You should see the planet "Soprano V" and a fleet of 2 ships as shown in the first screen snapshot below.
4. Zoom-out until you can see another Mimot fleet of 5 ships and an Iconian fleet of 20 ships as shown in the second screen snapshot below.
5. Click on the Mimot fleet of 2 ships and move them to the cell above and to the right of the Iconian fleet of 20 ships as shown in the third screen snapshot below.
6. Finally, click on the Mimot fleet of 5 ships and move them to the same cell where the Mimot fleet of 2 ships.  This will cause them to automatically join together into a single fleet of 7 ships as shown in the fourth screen snapshot below.
7. Do not do anything else and within about 10 seconds the crash should occur.

Hopefully, you will be able to recreate the crash and what you learn will help you improve your code.