Thanks for your feedback!
I did test all my scents, formulas, fo-loads and wicks before I started making them in batches so that was luckily not the problem :).
I actually figured out the problem was unfortunately with my nose, not the actual candles.. I had all members of my family smell the "scentless" candles and to them the scent was actually quite strong. After a long walk outside to "re-set" my nose I smelled them again and yes, I could smell them now, not as strong as my family described it, but the scent is there.
I hope this is not the beginning of the dreader candle-nose because going on a long walk every time before being able to smell my candles sounds very time-consuming..