This happened not the first time, it happens irregularly from time to time (I cannot recognise a pattern):
Selecting the blacksmith to collect my pearls I just got—as usually—the beautiful animation of pearls floating upwards and a big green «+483»—the problem is, none of them were added. I had as little pearls as before, but I lost the items.
Restarting the game does not help and with farms or taverns I never had this problem.
IGN: rs könig | RR2 4.5.0 | device: iPhone 8 / iOS 12