Welcome back. Let me share additional information about having incorrect check numbers in the bank feeds.
Before that, know that you can always talk to our live agents support since we won't always be able to provide a direct fix to the issue you're encountering especially if it needs to be replicated on your end. However, we're always glad to help and assist you with the information we have.
Please know that QuickBooks Online will depend on the information provided by your bank. Would you mind telling me your bank's name? Any additional details will help me provide you with an accurate resolution.
For now, let's manually upload the transactions to QuickBooks Online. This is to check if it's a QuickBooks issue or not. We can start by signing in to your bank's website, then download your transactions using CSV files. Make sure it's in the correct format. Once done, you can now upload the file to QuickBooks. See the screenshot below for the visual process.

You can also see this article that details the process: Manually upload transactions into QuickBooks Online.
If the check numbers are now correct after the manual upload, then the problem is in the bank. However, if it's still appearing as incorrect numbers, then I recommend contacting our QuickBooks Online Support team. You can follow the steps provided by my colleague. Please consider checking our available hours when contacting them to ensure we address your concern in a timely manner.
Once everything's good, you can now review and categorize your bank transactions and put them in the correct accounts.
Feel free to leave a reply below if you have additional questions or concerns. I'd be glad to lend a hand. Keep safe, and have a good one.