Let me guide you on resolving the error wherein every time you click an invoice, it shows you can't connect to the server. You'll need to ensure you have a fast and secure connection to open QuickBooks Online. Sometimes, your firewall might've blocked your connection to some websites, which might have caused this error to show.
Also, too much cache will cause some websites to run very slow and cause malfunctions. To troubleshoot any browser issues with QuickBooks Online, let's try opening it in a private or incognito window. Use these keyboard shortcuts to go to Incognito or InPrivate Mode.