It's in pure sphag? You need to be VERY careful with the watering then. Sphag holds quite a bit of water. If you are going to use sphag, then the goal is moist -- not sopping wet -- right after watering. Then do not water again until the sphag is almost dry (so barely moist) to a depth of about an inch (roughly the length of the first digit of one's index finger).

And yes, you should remove the glass jar. Moist, stagnant air is begging for fungal issues ... and if the media was overly moist, fungi are pretty much guaranteed.

This plant does perfectly fine in "normal" household conditions -- the higher humidity of the average terr is unnecessary. I grow mine as a regular houseplant -- in a pot on an endtable where it receives somewhat bright indirect light. Also I don't grow mine in moss. A mix of orchid bark mix and potting soil (the type WITHOUT fertilizer already added ( and boy that can be hard to find these days!) mixed in a ratio of 3:1 -- bark mix to potting soil -- has always worked well for me.

If it is rotting near the base, then yes, cut it above the section. You can dip the cutting in rooting hormone if you like. It is not necessary but shouldn't hurt. (Make sure you tap off any excess powder -- too much causes issues ... for most plants really.) Let the cutting sit unpotted for a day or two in order to allow the cut to callous over. Then pot it up in media which is just barely moist. Place it in a warm "bright shade" area. Should root up.

On the plus side, Ludisia is a fairly inexpensive plant -- or at least it should be. If you paid more than $6 or $7 for a single growth plant then, IMO, you paid too much. If, despite your best efforts, the cutting does not make it you can contact me. (I have several cuttings that should be rooted by now.) We'll work something out.

Good luck!