RQS Skunk XL on Coco under LED

The last 10 days or so have been a real struggle. Around day 10 I noticed the seedlings were a bit droopy. They were still looking healthy and were growing fast. They also tended to be less droopy after the lights were on for several hours. However, from day 13 they really started to droop. I was fertilizing twice a day and I noticed some algae growing at the jiffy pallets. The plants were in 1L fabric pots, filled with coco and 35% perlite. I figured overwatering couldn’t be a problem. The runoff measured around 1.0 EC and pH 5.8, so that seemed also in check. They were growing their 4th node and I figured maybe they were rootbound. On day 14 I transplanted them into 4L fabric pots (also coco and 35% perlite). When I transplanted, I found out the roots were completely underdeveloped. Just one flimsy central root with a few sides. There wasn’t a root ball at all. After the second plant, it became clear all the plants were in the same condition. To make matters even worse, during the transplant process, I damaged the roots. It was an impossible job to get them out of their 1L fabric seedling pots. I’ll never use a fabric pot as a seedling cup again (although, since there were barely any roots, there wasn’t a ‘ball’ that sticks together, which also makes it a lot harder). The whole process was pure horror. Why did my seedlings began to droop? Why were the roots completely underdeveloped? I fertigated twice a day (tapwater EC 0.5, EC of feeding mix 1.3, pH 6.4. I build up to EC 1.3 slowly, day by day) with a good 20% runoff (EC 1.0, pH 5.8). This strategy was based on information on the website Cocoforcannabis. However, looking around on other famous websites and forums, I found a lot of people having success with a wet/dry cycle on coco (but not completely dry!), at least for the first few weeks, to help the roots develop. Most people seemed to be using a root stimulant if they are using a high frequency fertigation strategy. With that in mind, I adopted a new strategy and fertigate every 2 to 3 days since day 14 (which is now 4 days ago). They are in 4L pots and barely have any roots, hence it takes a while for the coco to dry a bit. The plants have recovered a bit: only one of them is still really droopy, but the others look a little better compared to last Sunday. Recovery was and is also harder, since we have extremely dry weather, quite rare in my region. RH dropped below 35%. With some wet towels in the grow tent and the exhaust on the lowest, I’m able to push RH to around 45%. The lights are dimmed to around 40%, pulling 140 watts (320 being the maximum). Last: I’m still in doubt over watering was the only cause of my problems. Off course, the transplant shocked them hard, stunted their growth completely, but I already had problems before that. A lot of sources say over watering in a coco/perlite mix in fabric pots (and these were only 1L pots) is impossible. However, my coco was always wet and there was some algae growing around the jiffy pallets. Did I grow lazy roots? Is there anything I’m missing? How to get these plants to thrive? Any help would be really appreciated! Thanks and stay healthy! UPDATE DAY 20: On day 19, the plants looked a lot better, they were no longer drooping. However, another problem seems to manifest itself: there seems to be a deficiency, maybe Ca, maybe it's a general sign of underfeeding, since I gave them a low dose of nutes during te recovery period. Still under investigation, but I'm weirdly happy about it: suddenly they are growing fast and they look happy. Hunger is a good sign after a week of droopy, stunted plants that barely grow.