More likely a Watch problem. It may be hardware but there is a progressive hierarchy of remedies before resorting to the Genius Bar...
First force restart the Watch
i.e. press and hold both the side button and Digital Crown for at least 10 seconds, then release both buttons when you see the Apple logo.
Then, although it may seem irrelevant, while it is restarting Force Restart the paired iphone Force restart iPhone – Apple Support (UK)
Test it for a while. If it is still misbehaving... Unpair and set up again
Unpair and erase your Apple Watch – Apple Support (UK)
and then
Set up your Apple Watch – Apple Support (UK)
You may also want to make sure the software on the watch and iphone are both up to date to the same level.
Always update iphone first
Update your iPhone or iPad - Apple Support
Update your Apple Watch - Apple Support
If no better you may want to unpair and set up without restoring the backup
Make sure you are not using VPN or security apps on the iPhone.
If you've completed that troubleshooting and the issue is still not resolved, Contact Support.
Click here > Contact - Official Apple Support
or phone numbers
Click here > Contact Apple for support and service - Apple Support
and or Genius Bar Reservation and Apple Support Options - Apple