Some GPS receivers may malfunction on or after 6 April 2019 due to the GPS Week Rollover.
This is a known issue caused by the way that GPS used to handle the week element of the navigation signal. GPS used a 10 bit field to encode the week number in each GPS time message. This means that a maximum of 1024 weeks could be handled. This period is called an epoch. At the end of each epoch, the receiver resets the week number to zero and starts counting again.
The current epoch started on 1 August 1999. The next GPS rollover is 6 April 2019 when the receiver will revert to week number zero and start counting up to 1023 again.