Hi!

I'm not an expert but an enclosed terrarium doesn't need a lot of water. As it does a water cycle. I've been putting water in mine every couple of weeks or once a month since the soil and the container itself has been wet through. It might be that there's too much water the lighting needs to change (different types of moss need different lighting), or it could be that the moss is going dormant. Moss can go dormant for a long time.

Bugs on the other hand, isnt really advised for a terrarium as it won't be good for the plants. Perhaps, pick them out.

Just want to say as well, I love what you've done to it. Looks beautiful!!

Again, I'm not an expert but I really do hope this helps. Good luck xx

Are you using tap water? If so, that could be an issue. Tap water is often high in minerals and -- if it is "city" water, is often treated with fluorides and/or chlorides -- all of which can be detrimental to mosses. (And, particularly in a terrarium situation, many other plants too.)