I just experienced the same issue on my older Apple Watch. I figured that in itself was the problem and it was become a dated device.
I contacted Map My Ride a few hours ago and just got back this response:
“Thanks for writing. The minimum operating system required to use our MapMy apps is:
For Android devices, OS version 9.0 is the minimum requirement for the app.
For iOS, the device must be operating on iOS 16 or later in order to function properly.
For Apple Watch, the minimum requirement is watchOS 9.
After hearing feedback, we are working to change the Apple Watch minimum OS requirement to WatchOS 8.7 to allow users with a Series 3 Apple Watch to continue using MapMy and believe this should be out with our next app release.
This version should be released in the next week or two and will restore the ability to use the MapMy Apple Watch app back to WatchOS 8.7.”