Hi ive hade this problem myself!
I replaced thegauge 3 times each time it would last about 50 miles and then start fluctuating again.
The only concusions i could come to was:
1. The gauges are pants.
2. The vibration from the engine is wrecking the gauges.
3. A combination of the above two!
I asked JHP if they new what it could be and they suggested the vibration option.
I sold the bike!