The Analytics / Tag Manager dashboard has its own Dev tools as well apparently, so if you can see the code properly in the footer, AND you can see the calls going from your AtoM site back to Google, then I'd suggest following up in the Analytics dashboard to see what you can learn there, as well as digging into their docs.
Finally, one thing you could try is manually adding the tracking snippet to the _header file instead, in case it makes a difference. This would be a crude workaround until we can get things sorted and consistent on our end, but it might work if tracking isn't working as expected in the footer. Try following this, for example?
In the meantime, once we've managed to have an internal meeting, I will hopefully have further information. I hope this helps in the meantime with a bit of diagnosis!