I want to ask a couple of questions so I can provide you the best possible solution. Can you provide an image of the error message occurring and tell me what bank you have connected to QuickBooks Online?
I can assist in getting you the help you need in troubleshooting the error code being given. Sometime when receiving an error code, it means that at times, the browser data hasn't been cleared. The reason for this is because the first time you visit a site, the browser will save pieces of the site because the browser can display the files stored in its cache much faster than it can pull fresh files from a server. The next time you visit that site, the cached files will help cut down the page load time.
To clear your browser data you can go to Browser Data Cleared in QBO. I'll be here awaiting your response. Please know, I'm always here lending a helping hand.