Significant difference in calories calculation by the device or GC.
Two runs on the same route in April and June with similar pace (11.3 km/h and 10.8 km/h), similar distance (3.5 and 3.4 km), etc. result in 35(!) and 217(!) calories respectively. Average HR 131 and 148, which may be the cause but still it is not in any reasonable proportion. HR monitor has been unstable this year and gradually showing lower than actual HR.