The way UnifiedPush server sets the expiration date for messages when no TTL is specified is unstable. That means it changes with time (lowers to be precise). It is defined as a constant of about 68 years from the 1970 [1]. I've already filed a bug in the notnoop sender UPS uses [2], but it seems they do not resolve the issues anymore, thus fixing this directly in UPS would make more sense.

1 - https://github.com/notnoop/java-apns/blob/master/src/main/java/com/notnoop/apns/EnhancedApnsNotification.java#L62
2 - https://github.com/notnoop/java-apns/issues/147