According to Foresight News, SlowMist founder Yu Xian recently stated on social media that the loss of users' Atomicals assets was due to the burning mechanism in the official protocol. He explained that if a wallet or platform does not perfectly support the new protocol, the corresponding assets could be lost accidentally.
The official transfer rules for Atomicals state that the normal operation for ARC20 token transfers is that the sum of all input values should be completely or cleanly allocated to available outputs. In cases where there is not enough output value, or one of the subsequent outputs would result in over-allocation (i.e., token unit inflation), the remaining balance will be permanently destroyed or burned.