It doesn’t even have to be a bug. Having some rule like “invalidate all data older than 6 months” makes it easier to reason about and test for backwards compatibility.

I’m sure the data format of Apple Maps is constantly changing to support new features and optimizations.

apple maps data expires after 30 days.

if you create offline maps for some vacation away from reliable cellphone service, when 30 days passes the (gigabytes of) maps just disappear. Unusable even if you are in a remote village.