You say it had roots already? Air roots or more? If it was in orchid soil & moved to moss, be very careful it’s not too wet & rots the roots! I know from experience!! Lol. I would say if the roots are still fine it’s maybe humidity? I would also wrap plastic across the top of the pot w a hole for the stem to stick up thru so there’s higher humidity for the rooting itself, or use 2 pieces that meet at the stem if cutting a hole & fitting it thru is too tough. Don’t have gloriosum but have melano & splendid, & a bazillion other plants, but lost my first splendid cutting the same way. Covering the entire thing, leaf & pot, would be even better, but be careful because ppl say to forget about for days to weeks before checking it, but I’ve rotted stuff that way too, so I try to open everything every 24 hours or so for several minutes just to be safe. I mix perlite w my moss for aeration too & just make sure it covers the roots & node loosely but still allows airflow or that can choke it out too. My 1st thought is the roots but if they’re ok, increase humidity & cover the entirety or at least the moss & roots to speed up rooting. Make sure it’s getting enough light, & a heat mat speeds up rooting, but I don’t always use them (maybe should though & wouldn’t have lost some!) idk how much you’ve propped like that, but sadly you’re almost guaranteed to kill numerous things along the line~it’s how we figure it all out, esp since they all have their own preferences!! I prefer perlite in a semi hydro set up for most of my props, & have great success w that, including several I failed with other ways, but some absolutely do better in moss. Yet there’s been a learning curve there too. Maybe someone w a gloriosum will come along, but there’s a couple of fabulous rare & tropical plant groups on fb that can provide awesome advice & usually very quickly. Good luck~

Plant it shallow. Stem better seen on the surface, only root inside the soil. If it planted too deep, the stem will rot before it able to produce new shoot.