Some roots developing and some not?

Im 11 days into vegging.

i am running a DWC with a res temp of no higher than 18degrees at its peak and room temperature no higher than 26 degrees. 5.8 ph and i dont currently have a EC/PPM reading for you.

i am running Canna aqua vega with rhiztonic

some of the roots are in the bottom of the bucket and are fully developed to like a fist full and some aren't even out of the bottom of the nets, why is that? there's only 3 out of the whole lot but i am looking to flower soon but am waiting for these to touch the water. is there any way i can help them along? are the pebbles stopping them developing? any ideas.

As roots find dead ends/water/food sources they send signals to the main to send out new guys, As a fellow DWC grower this seems normal to me,
You can expect slower root growth with low temps as well, but I keep mine low as well

11 days Is not much veg time either, possibly use root enhancers/bennies on the clones to get a more vigorous start

How many plants? How big are your net pots? 11 days isn't too long, if you don't see any roots poking out in a few days it could just be slow rooters, I use roots xcelerator by h&g to help my slow rooting plants catch up