Try enabling the Authenticator app and then turning off 2FA.
This has finally fixed the issue for me and I can now turn it off and on with or without the Authenticator app. Something was messed up with my account. No amount of toggling 2FA would help. I was stuck in an endless loop of entering my six digit code every three hours. Everything now works exactly as expected and my browser is recognised as trusted even with 2FA on.
I took screenshots but adding images is a pain so the steps are:
- Turn on text message authentication.
- Edit two step verification
- Turn on Authenticator app
- Select your type of phone
- Install Twilio Authy or Google Authenticator
- Scan the QR code from QuickBooks
- Enter the code
- Turn off 2FA
