Very early in the game. Only met a single AI. We had trade luxuries on. I built an artisan quarter (first one) on a luxury.

At the same time as it was finished i had religious and cultural demands available on the AI's settlement.

But I kept receiving gold in 10 gold increments every few seconds, as it kept saying someone bought my resource, but when ever I looked at the resources tab it didn't show anything as traded. The tooltip was constantly popping up even after dismissed with the total collated so far, e.g at final point it reached ~800 gold for what was a simple 10 gold resource.

It only stopped happening when i demanded one the demands above, then withdrew it as they refused the demand.