Security Key app not working

My husband and I just got new phones yesterday and we are each having the same problem: the security key app, that we had been using on our old phones, does not work on our new phones.

Old phones: LG G3, with Android 6.0.
New phones: LG Stylo 3 Plus, with Android 7.0.

We followed the steps for removing the registration for the app from our old phones, as provided at this page (which is also provided in the pages in account admin about registering and using the software token). But when we each open the app on our phones, we get nothing-- just the screen for the app with the little "loading" keyhole icon, and nothing else happens.

I was hoping someone here might have had a similar issue that they managed to resolve.

I have the LG K20, sure it's a bit of an older phone, but still runs Android 7.0 Nougat. I did have to remove the software token via the page manually first as well, and then install the new APP. However the first time, same problem as you guys, it didn't load or so I thought. I removed it and installed it again, same thing. I then opened the APP and went on with my life, after 10 minutes it did load the "welcome to the security app" screen and let me put all the information in. It seems the first time it gets installed, it needs a specific amount of loading time, not sure why but try that. Open your APP leave it alone for 10 minutes, check up on it, might have to close it one more time and run it after. However after that's done, the APP works without any issues and loads within seconds, just that initial after install opening seem to take it's sweet time lol.