Whether you have not connected a wallet or exchange, have not confirmed the internal transfers in the review steps or the internal transfer has not been recognized due to an issue with the data, an internal transfer not correctly connected and classified will result in the transaction showing up as a taxable disposal. An internal transfer is a transfer between your own crypto accounts / wallets - a transfer to yourself. If one half of this transfer is not connected, the data may look as if the crypto was sent to a 3rd party as payment, therefore the default assumption is a taxable disposal.
The best way to recognize this problem is to first ensure you have completed Step 2 of the Review tab. If issues still remain, locate the transactions triggering the incorrect tax and identify if the issue is linking a missing wallet or if the other side of the transaction is not being recognized and take the appropriate steps - link the missing wallet or make sure both sides of the internal transfer are made within a 6 hour window, for the same currency and for roughly the same amount within an immaterial difference.