It appears as though some of your creatures found that they lost their magical ability to walk anywhere they wanted! Creatures have had their restricted terrains updated from being only restricted from volcanic tiles to be more in line with what was intended/realistic. Some of you may have creatures that are stuck on a terrain, due to this, and my first suggestion would be to move your ship/vehicle/station(if you can bring it with you!) onto the same surface square as your creature and try to load it. If you're unable, please submit a support ticket, and I'll move it for you (I may regret this). A synopsis of the changes is below. If you feel strongly enough about a restriction being/not being in place, also let me know. Thanks to Cedron for the idea, Lucas Isen for assisting with compiling the list and to Noctis!
EDIT: Late night oversight made me overlook all the crater restrictions. I will revisit them tomorrow.
EDIT 2: Ok, restrictions have been thoroughly combed through, and some liberties were taken to allow creatures to (in general) sometimes go on terrain they may not traverse normally, in an attempt to keep things semi-fun for the player. If there's any glaring issues, please let me know. The pictures above have been updated to reflect the changes and should be correct.