Stefano1,
How cold is it in the room where your plant is? Generally slow trap movement is due to lower temps... also, sometimes they experience a bit of shock being unpacked and removing the plastic cover. They do come back around pretty quick... but it's something that we've experienced over the past years.
If the trap doesn't close all the way, the bug will not be digested. If it does open back up, remove the bug so it doesn't cause mold or fungus to grow.
If the bugs were dead when you put them in the trap, they won't close all the way, or will open right back up in a day or so. If you feed your plant, keep the insect barely alive, so the plant knows it caught something alive!
Hope this helps!