Note this game has a bit of modding done;
my Ark is extra powerful.
I spawned a bunch of ships and destroyed the enemy defenses on the first planet.
I then captured it, bumped the AI Progress up to 250 and then
spawned a wave; I conjectured that "more things" in the galaxy would
allow me to find the problem more quickly.

At 9:25, here is top output for the program (about 2 minutes after I paused)
KiB Mem : 16199336 total, 12496904 free,  1131964 used,  2570468 buff/cache
KiB Swap:  8191996 total,  8191996 free,        0 used. 14626900 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND     
 3416 wdavis    20   0 4349316 399868  68896 R  75.0  2.5   3:18.98 AIWar2Linu+ 

I also saved the game at 9:28, in case that's of use