I can only really suggest what I'm doing to my Macro. As you saw the setup, my temp drops are not very drastic, maybe 8 degrees here in summer, 10 to 12 if I'm lucky here in the heat.
I leave just that little lids on my smaller neps though. I try to have a wind current at all times around my neps, but I think for small ones like these it's too much especially since they are just walking out of flasks. I don't feel these dime sized ones can barely take any fluctuation.
Also I just water mine roughly 2 times a week. Goal is to keep it moist but def not soggy.
How are you applying the frozen packs? Perhaps the cool packs are making things dip too rapidly or too far, especially if it's changing the soil temp. (ie the plant is sitting on the pack)