Maybe theres other scenarios that give no gold on disco of new (to you) city state besides the multiple declare war on CS = no gold discovery
Kinda rare, I'd say maybe only a few times in last couple dozen games - so not common - but I've never declared war on a CS, ever - and had my unit discover a new CS I hadnt met before and recieved no gold.
Never had this happen in early game, but seems like only around mid game or later, if for example playing continents map and had turtled up / isolation, so hadnt explored other continet till industrial or later.
The weird thing is its not every CS on other comtinent that doesnt give gold, its like just 1 or maybe 2 max on entire standard size map that for some reason doesnt give gold on discovery.