I completed a game of Entrenchment and noticed a few minor thigns. But one major thing:

Let's assume my credit total goes up 20 credits per second. Let's assume It's at 260, and ticking up, and at 300 I want to build a cobolt frigate. When it's supposed to tick to 300, it went down to 217 instead. Then I waited for it to come back up and built the frigate. I observed this in the mid- to late- game. Happened a few times. Always seems to be a drop of between 60 - 100 credits.

thoughts: could it be a trade transport being destroyed? I had a planet under seige by pirates for a while, and a trade port was in the system during this period