Are you using Evens Waterless Coolant? If so change to Prestone 50/50 pre diluted. Evans is no longer approved by Rotax. There should be a label on the top of you coolant reservoir if you have Evans. Evans runs significantly hotter temps.
Just experienced the same. Tach time is much higher than it should be. Hobbs appears to be accurate. Sent a diagnostic file in today. One Flight today showed .9 hrs. Hobbs and 1.2 hrs. Tach??? Second flight showed both Tach and Hobbs at .3 hrs? Third leg showed Tach 1.2 and Hobbs 1.0.