Japanese calendar era bug

The Japanese calendar era bug is a possible computer bug related to the change of Japanese era name.
Background.
The Japanese calendar has Japanese era names that changes with the reign of the Japanese emperor. Since most of the modern age of computing has occurred in the Heisei era, much of the software developed in this era only has support for era names during the Heisei era.
A new era name was expected with the forthcoming 2019 Japanese imperial transition. However, since the change of eras is infrequent, most software has not been tested to ensure that it will behave correctly with an additional era. Computer and software manufacturers need to test their systems prior to the transition in order to ensure that the new era will be handled correctly. In order to ensure this, some systems provided test mechanisms to simulate a new era ahead of time.
In early April 2019, the new era name was announced to be Reiwa for "beautiful harmony."
Documented errors.
Some minor problems have been reported due to improper handling of the era transition.