V 1.7.2

Cities that have already tiles on the resource fields can't build the extractor tile after unlocking it until reloading the turn.

That's intended. You need to plan ahead with your burrough develpment.

I don't think you understand what he means:

So, he unlocked the extractor with the blessing, and now he can't build on an Adamantian Vein which is next to a borough (so, exploited by it but nothing built directly on it, excluding a normal extractor). When he reloads the game, he is then able to build the extractor, but as long as he simply keeps playing, the extractor stays locked.

At some point I was so annoyed by it that I build a borough over that recource field - next time I will know that a reload will fix that issue :)

This was reported during the Sybosis beta, the Devs said they would take a look at it. I would guess the fix for this will be part of the next patch.