The GPS system includes a week number, starting January 6, 1980. As it’s only a 10-bit number, it rolls over to 0 every 1024 weeks. It happened on August 21, 1999, and will happen again on April 6, 2019.
Both the u-blox MAX M8 (AssetTracker v2) and the GlobalTop PA6H (AssetTracker v1) will continue to work through this rollover.
Both will require a software update before 2038 when the next rollover occurs, however.