Hi @Jonny Donovan,
I'm here to point you in the right direction for support about your query on online bank connection.
Since you already went through the troubleshooting steps as well as the workarounds shared here, then I suggest contacting our Technical Support team for further assistance. They can investigate it further why you keep having this issue after all the steps you've gone through. They can then isolate its cause, and provide a solution for it.
Visit this link for the instructions: Contact QuickBooks Self-Employed Support. It contains different ways you can get a hold of technical support.
You can keep this article for future reference as well: Support hours and types. Each type of support for every Intuit product is listed, along with their operating hours so you won't miss them.
Direct other questions in the comments below, if you have any. I'll be sure to get back to you.
