Hello there, @hello12.
When you reconnect your bank in QuickBooks Self-Employed, you may notice that all your transactions have been removed. This happens because when a bank is disconnected, all transactions, including the categorized ones, are also removed.
However, you can reconnect those transactions that have been removed by manually uploading them. Take note that only transactions within the last 90 days can be downloaded and connected. Here's how:
Additionally, if you need to review your bank transactions in QuickBooks Self-Employed, you can check this article if you need help: Categorise and match bank transactions in QuickBooks Online.
Should you need additional assistance in managing your bank transactions, feel free to include them in the comments below. Keep safe!