I have done all of those research, there was an improved Trader upgrade in the last chapter, and now again in this chapter. It is accumulating goods from another building that I have but not from the Marble and perhaps not from the Steel when it's upgraded enough. I've just done a collection and there should be at least a couple thou of Moonstone
This seems really mysterious to me! That other building which gives you Tree Gum is probably an event building I guess?
Event-Buildings sometimes make it possible to gain for example troops or goods, you haven't even researched yet, like the Creepy Clinic in todays event - even if you would not have reserached "Rangers" yet, you will get some of them out of this building every 24h.
As those accumulations of Tree Gum are not really produced but only, I would like to say, given there is no problem with them arriving in your storage, but don't worry as far as I know you will lose none of your Moonstone you've already produced.
I guess it's just because that your humans and elves in your city don't know how to handle those "new" goods as long as your
Advanced Trader isn't upgraded to
Stage 3.
After having the Advanced Trader upgraded to Level 3 the people in your city finally know about what that new seninent stuff in storage is and your storage should display the amounts you have already missed before.
This Upgrade unlocks the first Sentinent Goods, so you will be able to trade them - that's probably why you cannot see them in storage yet atm.
if I understood you correctly you haven't upgraded to Stage 3 yet?
Just upgrade your Advanced Trader to Stage 3 and you should be able to see all 3 amounts plus being able to trade them on the market.
Edit: Of course,
@Ravmin supposition could be possible too, As only the prodctions "Demetor's Bowl" and Ignita's Gate will deliver Moonstone, you could haven chosen the wrong production by accident?