IPhone and Apple watch are shutdown / reboot randomly at same time

Unfortunately those crash reports require a computer to analyse them, we cannot help.

My advice:

(a) Unpair the Watch

(b)Backup the iPhone

(c)Reset the iphone to factory settings

(d) Set it up again without restoring the backup

Only install the most essential software, or preferably no third party software at all. Add back your mail accounts by all means.

(e) Pair the watch again

Run it for a day.

If the problem goes away, repeat steps (a) (c) (d) but this time restore the backup then (e)

If the problem comes back then you know what the cause is.

Resources you need: (Allow a couple of hours for each session)

(a) Unpair and erase your Apple Watch – Apple Support (UK)

(b) How to back up your iPhone, iPad, and iPod touch - Apple Support 

(c) Restore your iPhone, iPad, or iPod to factory settings - Apple Support

(d) Set up your iPhone or iPad - Apple Support

(e) Set up your Apple Watch – Apple Support (UK)

Make sure you have no VPN or VPN based ad-blocker on iphone. Uninstall them then remove any profiles (iPhone Settings, General VPN & Device Management)

Then reset the router to factory settings which usually involves a paperclip in a little hole. 

Then in the iphone, Settings, General, Transfer or reset iphone, Reset, Reset network settings. 

Reconnect the iPhone to Wi-Fi and try again

If you've completed that troubleshooting and the issue is still not resolved, use the link in the article to Contact Support. 

Click here > Contact - Official Apple Support  

or phone numbers  

Click here > https://support.apple.com/en-us/HT201232 

Or

Click here > Genius Bar Reservation and Apple Support Options - Apple