If you have a large queue of mine deployment, you can cause something like this. Mines cost money for Advent to deploy, so if you told a whole bunch to build somewhere, as soon as you get enough money, (about 600 credits? trying to remember), they will deploy and suck it out of the bank in a chunk. This will keep happening until all the queued mine deployments complete.
In regards to the other posters, Pervasive Economy doesn't suck away other people's credits, it just boosts your own. Sova carriers don't steal it in chunks either, they steal from your income rate, which could possibly put you negative. If you are negative from this or undeveloped planets, you tend to see it drain kinda steadily, not in big chunks.
I can't really think of what else it would be....
