Note: this workaround only applies to iOS 13.4 and later
Every app gets only one chance to ask for Always. It can use it directly as the first ask, in which case the app will wind up in Provisional Always auth mode, and get the deferred prompt eventually, which is what you are complaining about. This prompt will always arrive when there are no apps running in the foreground.
Apps can also ask for when-in-use first. And then ask to upgrade to Always, once the user is familiar with the app more, and have a lower chance of being rejected at the prompt.
On iOS 13.4 and later: the user will see a prompt for upgrading from when-in-use to Always immediately, over the app which is asking for the authorization.
Asking for when-in-use first, and only ask to upgrade to Always (if it turns out you need it) is the preferred way of doing this.
In 13.4 this strategy now has the added benefit of eliminating the Provisional Always period while the app waits for the system to prompt the user sometime in the future. The benefit for those apps will be that once the user agrees to Always at that point, the app will have full Always authorization.
Of course, you should be careful in using this technique, as asking for this two step permission back to back will create a jarring experience for the user, and may end up them eventually rejecting your request.
All this, though, still does not change the fact that the users will be reminded periodically in the future that your app has been using their location in the background. Those prompts will always arrive outside of your app, and there is no way to stop them from appearing.
