GREAT NEWS!
The Runkeeper version 8.7 update from 7 feb 2018 is addressing this issue:

"Guess what! We redesigned and rebuilt the Apple Watch app. We squashed some tricky GPS bugs, greatly improving the reliability of Watch trips. We’ve listened to our users (hey that’s you!) and we think you’re really going to like this update.
New
- Dedicated heart rate screen to show zones <3
- Splits alert with quick comparison
- Post activity stat summary
- Recent run history for Watch runs
- Use your Watch as a remote when tracking with your iPhone
Improved
- GPS performance and reliability
- More glanceable stats, easier to read while running
- Simplified settings with countdown option
- Better Watch only mode—start a run from your iPhone or Watch
- Recent run history for Watch runs
- Use your Watch as a remote when tracking with your iPhone
Improved
- GPS performance and reliability
- More glanceable stats, easier to read while running
- Simplified settings with countdown option
- Better Watch only mode—start a run from your iPhone or Watch