It happens occasionally, that specific ERC20 token at certain point in time migrates from Ethereum Blockchain, where it exists as an ERC20 token to own blockchain. This happened for example with TRON and EOS in the past.

In such case you have to follow the transition advice of the specific token issuer.

You have to be careful though not to mix up legacy ERC20 Tokens and own blockchain coins under same name.

For example with TRON (TRX) you can distinguish the two by the format of the wallet address:

Legacy ERC20 TRON Address - 0x939a715B25308f56Ed17Fa60fC88556E77B83602

TRON Blockchain Address - TF5ko6qZ7dQPaPNhNyurgL8RcYeB8MQXeh