Apple:

Apple has determined that a very small percentage of iPhone 8 devices contain logic boards with a manufacturing defect. Affected devices may experience unexpected restarts, a frozen screen, or won’t turn on. Apple will repair eligible devices, free of charge.

Affected units were sold between September 2017 and March 2018 in Australia, China, Hong Kong, India, Japan, Macau, New Zealand, and the U.S.

If you’ve got an iPhone 8 and you are experiencing these sorts of issues, follow the link and enter your iPhone serial number to see if your device qualifies for the program.