Unfortunately, the process android.process.acore has stopped error generally occurs due to outdated version of Android OS, corrupted cache data of the Contacts app, insufficient storage space on the device, glitches/bugs on the phone, etc. However, restarting or updating the phone, clearing the Contacts app cache, and removing & re-adding the Google account are a few ways to fix this issue. Nevertheless, if you want to know more solutions to get rid of it, read this article till the end.