I have to agree with you on the temperature differences, I was disappointed when I didn't see 17a readings in July when it was 24-27C/75-80F. Saturday morning everything was frosted and it took a while to warm up. Had I thought to wipe down the panels after the frost melted I probably would have seen more. We never saw frost again or 17a. High 16's though.
As for the Eco-w being affected by temperature. I've seen asked if it has TC on you tube and the person that responds as Eco-worthy said no. I've seen it respond to high heat by clipping amps and I get higher readings when it's cold out. Yet you didn't change it with a Ice pack, so the difference has to be the panel unless the controller gets really warm. It's possible it clips amps then as a self preservation act to keep from burning up.