The building blueprints sometimes disappear without a trance. I’ve had this problem multiple times that I prepared all the materials, but the blueprints have suddenly disappeared. Please fix this problem. It’s a bit annoying . Thanks.
This issue has been reported for the entire 11 year life of this game and EA has never been able to fix it. Here are some of the first reports about this problem, for example.
Building upgrades disappearing | EA Forums - 10379442
SimCity: Yellow hat upgrade icons disappear for no reason | EA Forums - 10403134
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