Thanks for getting back to us and sorry to hear that the workaround is still resulting in that strange error!
As mentioned in one of my earlier posts, we can't guarantee that non-Rogers devices will work seamlessly on our network. Unfortunately, there is always the possibility that some functionalities won't be accessible. 😟
I was reading up on another third party forum that a user with a similar issue found a solution that worked for them. Whether or not this will actually work for your circumstance, I'm not certain. What they indicated is that, instead of tapping the "save" button, try backing out by selecting the "home" (circle) button, and once you go back into your APN list you should see the new APN setting saved at which point you can select and enable it. Perhaps, give this a try?
As a last ditch effort, if there is a current APN already listed in your settings, you could also try editing it to our settings rather than creating a brand new APN entry.
If anyone else in the Community has any advice to share, please do!