Some suggestions and observed issues, based on a couple of 1.13 games:
1. The Swarm is too variable in the danger level it poses, and can be far too deadly. What deep-space bugs should not do is a) scout your home planet (>10B km away from any jump point or linked LP point) five years into a game, park 10s of thousands of tons-worth of warships in orbit a few months later, destroy all your shipyards, and start bombarding your helpless early-game homeworld to dust and ruin. Endlessly, because they never run out of supplies.
This is unfair, because:
a) The player, if they set up using ordinary early-TN tech levels (the ones the game offers as defaults), may well not be able to fend off such an attack so early on. "You lose. Regardless of any attempt you might have made at preparedness." is not what a game should tell players. This applies also to the Invaders.
b) Distance should matter to the AIs. If the AI can't be made to understand fuel limits, it should at least respect a travel distance limit.
c) Supplies should matter to the AIs, at least in some sense. They don't have to run out when attacked, but if attacking, they should not be able to fire beam weapons endlessly, especially when bombarding.
d) If it is intended for space bugs to be a mortal threat, or at least if they should attempt to wipe out players if not stopped, then the game should provide some sort of warning that these aren't just ship-killing, wreck-harvesting critters ... the Swarm wages wars of extermination!
2. The bugs or game design choices that trigger lengthy - and in some cases quasi-endless - runs of increments measured in seconds, when the player is not involved, need to be hunted down and put of players' misery.
a) Are all fire controls being properly cleared when a target is lost or no longer available?
b) Can AI-versus-AI fights be resolved using a simplified set of rules? "If on attack and not in range, but might be able to get into range, chase until in range. Otherwise, defend. If has missiles, and missiles can't be shot down well enough, subtract missiles and inflict damage. If has beam weapons, and can catch target, catch target and inflict damage. Otherwise, set to chase or defence, and counter-fire only. Repeat for all other sides. Repeat for each suitable sub-block of time. Stop when all but one side is destroyed or escapes, or all sides are on defense, or the player-specified block of time ends." That kind of thing.
c) If a) and b) are not sufficient, then at least allow the player to learn which fleets are killing game progression, so they they can be deleted. Make it easier to kill off fleets without triggering "not set to an object" error messages.
3. On the subject of those dratted error messages: The keystroke used to clear the message should not be the same keystroke used to request another turn increment. At present, both are ENTER on my keyboard. Extra credit if the error message could be presented without popping up a box, and/or if the game got better at deleting objects that trigger such messages. For example, if a ship can't find its fleet, maybe kill off the ship?
4. The game interface redraws windows and refreshes text extremely inefficiently. This is immediately noticeable on the message window. The Economics window also has a problem here, a problem worsened by its refreshing every turn increment (even if only 5s) instead of just doing one automatic refresh every construction cycle. In long games, the Leaders window and even the Ship Design window can also bog down.