When choosing "stop syncing and keep data in a new manually-managed account" for one account in a connection with multiple accounts, the other accounts under that connection get irreversibly revoked once the next sync attempt occurs.
To reproduce this:
  1. Connect an bank account with multiple accounts (eg. Checking, Credit Card, and Savings).
  2. Select one account and choose "stop syncing and keep data in a new manually-managed account"
  3. Go into one of the remaining active accounts and click on "Triger refresh"