I'm facing the same issue. I need to connect BOTH the parent bank account and the sub-bank account to QBO. As there are some transactions that only show on Parent Bank. Like payback to the parent's credit card and interest charged on the parent's credit card.

If I cannot see these transactions in QBO, I cannot categorize them and cannot reconcile the bank transactions.

I want transactions to appear in their respective parent or sub accounts, not mixed up.