There are 2 things I can share, which might help you to solve the problems. At least, they helped me:
There is a bug in the Order Class which brakes the WebService, and it is documented here: PSCSX-4403 and PSCSX-4423 The fix is described here.
Orders cannot be filtered using "current_state" filter anymore. (The system returns error that this filter is dynamic (?) and cannot be used) So, if you were using it in the calls to API, then you have to redo/reprogramm your codes. You can pull out all the orders and do status check of each of them one-by-one.
I hope this helps.