Apple has announced that it is offering free logic board replacements for affected iPhone 8 devices purchased between September 2017 and March 2018 in select markets. Apple said that a small percentage of iPhone 8 devices had a defective logic board that resulted in unexpected restarts and frozen screens.
https://www.notebookcheck.net/Apple-offers-to-repair-defective-iPhone-8-logic-boards-for-free.328552.0.html