I've been keeping marcgravia for about a year now so i'm not an expert but this is common in my opinion. When I put cuttings directly into vivs it almost always loses half to most of its leaves before taking off and doing well. I have had some that just die as well. I have found that if I root it in a prop bin on spaghnum without ever getting the leaves wet but keeping humidity high it does much better transplanted into vivarium conditions. Generally I think if it has roots it does much better as opposed to just putting in a cutting. Species I have include rectiflora, red and white umbellata and sintenisii.