Playing Thalan on an Excessive Map, under victory conditions saw that I needed to control another 7% of the Galaxy for an influence victory. Queued up some more constructors, built more influence buildings, set completed planets to Cultural Festival, save game.

On resumption; now need 13% for influence victory, and 5 turns later, even with more culture starbases/buildings complete and no expansion whatsoever from enemies or allies, it's only at 11%. I was kinda scared to save and exit again, in case it drops me back even further! No event came up, tech I'm researching is just on the Warfare branch, didn't lose any influence resources.

Anyone else had this happen, or even better, know why it happens?