From your original post it looked like you were still experiencing reboot issues, my apologies for the miscommunication. What firmware are you running? If it's stable enough to update the FW, try getting an automatic update by going to Settings > System > System update. You can also do a manual download for your region, the guide on how to is here
https://www.asus.com/us/support/FAQ/1009748/, and the download link is here
https://www.asus.com/us/Phone/ZenFone-6-ZS630KL/HelpDesk_Download/.
If that doesn't help, then the advice to contact your repair center still stands.