Underwatering not solving ;/

Plants look fine, not sure why you are worried. Yes, water entire pot until run off then do not water again until the top inch to inch and a half has dried out. Repeat this for the entire plants life. If you do this, you can't go wrong. Watering specific amounts, ie 500ml, is not the way to do it. You will have to decide on some fancy training soon, you are growing 4 plants in an area that is really only siutable for one.

First, let's fix some potential misconceptions and habits. Watering s easy. 1) water entire pot -- you do not pick the volume, you give enough to saturate the entire thing. 2) wait for top layer to dry and repeat. this is diffrent for differing water capacities of the substrate. With a 'soil' you wait for top 1" to dry before repeating. something lke coco coir holds 2/3rds the water per volume and you water a bit sooner than that dry back. Regardless of substrate used, if you irrigate at same loss of weight, it will require the same volume of water. you cannot fuck up irrigating if you follw these simple concepts. If you get any droop after irrigation, that's due to a poorly constituted medium -- more perlite or similar is needed to avoid drowning roots from basic watering habits. Any problems seen will be about your choices of fertilization and not your irrigation habits. over/underwatering is easy to avoid. simply don't do it. You can fix your habits now, but if your substrate doesn't have goodo drainage properties, you can't really add extra perlite midstream. could add more to any up-potting that remains.

I see no diary with conditions. If medium gets too cold can prevent or slow the conversion of nitrogen. Heat and air. More temp more air. She looks healthy just need to give her a poke.

Fabric pots sitting on ground not recommended. Especially if it's concrete floor can get very cold. Need to have them sitting in catch basins, i also do not see any airflow hitting those fabrics, water evaporates or uptakes through roots, if the rh sits higher than ambient 50% consistently then water within the medium is there is a chance the water will stagnate at bottom of pots.

What I think has happened is that she had a bit of a shock going from a dry medium to wet and then you overwatered her. 500ml in a 1.5l pot shouldn't be excessive, but some plants are Primadonna's and the pressure change can get them to droop for a while. This is not a problem if you just leave them for a while, they balance again and go back to normal. Adding more water was not the best idea as it has only made the issue worse and potentially oversaturated the soil. Now there is very little oxygen in your soil and the roots are struggling for air. Luckily your bags are slim, so they should dry relatively quickly, so just don't water again till a few days after she recovers from this.