Hello i have a iphone 8 with ios 11.4 and it has been shutting down randomly. Have tried doing a full clean wipe and it still does it. Try turning it on after crashing it will be in a boot loop or or show battery critical and needs to be plugged in, sometimes if i do get it going the battery will be around %10 and if i reboot it with the plug in the battery level will go back to where it was. A couple times it has crashed while plugged in, please help its getting really annoying
At this point you will need to book a appointment at the closest Apple store to you and have a genuies rep at Apple look at the phone. They will diagnose it for you and will either replace the whole phone or so wavy they can do.
I'm sure random shutdowns can be quite disruptive. Typically new devices come with a 1-year manufacturer's warranty. Since you do not have Rogers Device Protection, I would recommend you to reach out to the manufacturer as was suggested by Meowmix above.
Please let us know if you have any other questions or concerns.