
Drop the feature completely!
What would be the downsides for the user, if the IDFA would change on every request the app is making for it? The device/app id for features like "You were using this account from these devices" is not necessarily affected by this, on iOS, you can use your application's VendorID instead. though you will not be able to fingerprint across reinstalls of your app, which I consider a feature.
This somehow feels like a discussion about how much crap can be reasonably swallowed by the average customer - What is the benefit of having IDFA at all from my perspective? No, I'm not an advertiser...