from cold and dark the L1 stair. Before update, GSX was capable to remove the stair, because understand that you have a jetway.
On the 737, GSX uses the 2nd FMC to remove the stairs, and in cold and dark, it has no power until you turn at least the battery on. If the FMC is not powered, neither GSX nor you can push its buttons, but the change from using the 2nd FMC from the first one happened long before this update, so I can't see how GSX could have possibly been able to use an unpowered FMC.
I guess we might "fix" this by checking first if there's any power (real cold and dark), and in that case use the 1st FMC instead, but never had this logic before.
The reason why the PMDG 737 stars in cold and dark on a gate with a jetway with a stair attached might be a quirky, but you should be able to prevent it, by sending away they stairs manually once, then Save this as a new custom cold and dark preset, which you can also make as default or not, if you want. If the save state works as it's supposed to, you will never start with the stairs attached.