Darkness Resistance upgrade cost - bug No. 2,178,535,950

First, I take a look at the cost of the next upgrade my Darkness Resistance and I see the following:

The cost required to make the next upgrade is 1021 pieces of azurite.

After I gathered the required amount of azurite, I see the following:

As you can see, when I have enough azurite on me, Voltaic Generator gives me much lower cost for the same upgrade - 491 pieces of azurite

Meantime no other upgrades has been done at Voltaic Generator.

sorry, but look closer at your pictures -->
The first cost is for a upgrade on level 47 and the next one is for a upgrade on level 55.
That is also why your resistens have dropped even more then is was before so you have pay more to get more. :)