HCA: Hermit Crab Association

We brought two hermit crabs home from the beach in early July of 2023.
In August, they spent the whole month under the sand. (we have a camera, they never came up) Went down August 6th and came up Labor Day weekend. They stayed active through Thanksgiving.

Thanksgiving weekend, we upgraded them to a new bigger tank, with a deeper sand substrate for them to play in. That weekend, they both dug down and we haven't seen them since. (again, camera, no movement at all.) There is an entry hole that we think they both followed each other into, but no other signs of them even crawling around underneath.

Is it possible that they molted in August and again in December?
Do crabs de-stress for 4 weeks or more at a time? (seems long)

Thank you.

For sure it is possible that they are molting again. You didn't say how big they are, but unless they are large or jumbo, you can expect them to molt every couple of months or even more often than that!