Hi there, @RayW,
First of all, I appreciate you contacting our support team to help fix the error when turning on the MTD last week.
I've checked here on my end if there's an ongoing investigation about the "The VAT accounting dates don't match up." error and it's still open. Our product engineers are currently working to have a permanent fix.
In line with this, it'll be best to contact our QuickBooks Online (QBO) Support Team. This way, one of our specialists will add your account to the affected list of companies. They'll be able to notify you about the issue's status via email. You can reach out to them through this link: QBO Customer Care Team.
After the investigation will be fixed, you’ll receive an email within 72 hours to confirm that you can submit returns using software that’s compatible with Making Tax Digital for VAT. Here's an article you can refer to: Making Tax Digital for VAT.
That should point you in the right direction. Stay in touch with me how it goes after contacting them, @RayW. I'm only a post away if you have any follow-up questions or concerns.