Power from 4iiii outside and Kickr Core inside

30% is indeed a pretty huge discrepancy. My 4iiii left side crank reports about 0.9x what my Core does (and I’ve had four KICKR Cores due to various mechanical failures- all had approximately the same multiplier offset compared to the 4iiii).

DCRainmaker has a pretty good article on this. Don’t expect this to solve your problem, but it does discuss some of the tests to do and how to analyze the data in a little more depth to get to the bottom of it:

Also, a great discussion on these forums about how your KICKR is estimating power (Spindown/energy) vs. your 4iiii (Strain).