u/Double-Bus-1854

Hi everyone, I am new to posting on Reddit but I have a question and didn't know where to ask. I have owned hermit crabs for a few years now. I currently have 6 in a 80 gallon tank, humidity and heat but within normal range. We had a colder winter where I am but the tank heat dipped to ~74 Fahrenheit at it's lowest and humidity never got below 75%. I noticed that a few of my crabs have been under the substrate for longer periods of time especially during the winter months. They periodically came up throughout the winter but I've noticed I really only have 2-3 that are regularly above the substrate. There are 3 I haven't seen for ~2 months now. I know they could be molting so I have not disturbed the substrate. I wanted to ask if people have had the crabs under the substrate for a long time because I am getting a little anxious about how long I haven't seen a few of them. I just really haven't had one go under for longer than a month. Any insight is appreciated, thank you!