Metamask charges transaction fees (in part), but does not transfer money, citing some kind of error on the network.
I wrote to those support, they replied that it was not them, but the fault of the Blockchain. No refunds are given for transaction errors.
Overall, Metamask is most likely cheating, but not admitting it. If 0.5 dollar is stolen from one client - this is kind of nonsense, and if from 1,000,000, then this is the amount.
They could well have written a bot to steal money from clients little by little ... Or they have a "leaky" transfer system ...