After a device is wiped and re-enrolled, it is no longer in the original static group. Seeing a device remove from a Static Groups after wiping is expected behavior. When devices are wiped and re-enrolled they temporarily get marked as unmanaged in the database until they finish enrollment again. Since Jamf Pro cannot put unmanaged devices in a group, they get kicked out of all static groups.

Device will need to manually be re-added to the static group after re-enrollment. For more information see, Static Groups.