Hi Smanfer,
Thank you for using the Apple Support Communities! I understand the Region setting is reverting to a different location on its own. I'd like to explore this further to help.
I have a few questions to gain more information about the behavior.
-Was either your iPhone, or Apple Watch purchased in the United States?
-Do you have your Apple Watch set up to mirror the region setting of the companion iPhone? Open the Watch app > General > Language & Region.
-Is your date and time accurate in your iPhone under Settings > General > Date & Time? Set to Automatically? Change common iPhone settings - Apple Support.
-When you first began to notice this behavior, were there any changes to your iPhone around the same time?
I would then recommend trying the following steps in an attempt to solve this:
-Restart your iPhone: Restart your iPhone - Apple Support, and Apple Watch: How to restart your Apple Watch - Apple Support.
-Update to the latest iOS: Update your iPhone, iPad, or iPod touch - Apple Support, and watchOS: Update your Apple Watch - Apple Support.
Keep me posted. Regards.