I just want to add that after reading some posts, a note that comes to my mind is:
If I ever want to move the ants, perhaps the best way is to connect the old nest and the new nest together with a connection tube and let the ants decide on their own. Perhaps with this method, they can choose (as in investigate the new area and see if it's good and safe). Maybe the new nest somehow had something in it that we can't sense but they can and something is wrong.
Not knocking on the quality of the nest, I hear honeypots are the more fragile of the bunch and have heard some fails after the first year.
One of the things I heard is people running them a bit too hot. I keep two ants and I try to run them on the lower side of the range. Like if my ants live in a range of 75-86F, I'd always go somewhere closer to the low end around 76-77F.
Make sure the food that you're giving them is free of pesticides or contamination, such as questionable fruits or honey. Hope you also keep them in a dark, quiet place. Vibrations and light will bother them.
Was the mini hearth way too small for them? A bit crowded is fine, you should've seen my nest, they were packed and when I opened a new nest on the side, they kinda stayed in that one nest all packed up and tight.