Problem

in reception : error 904 Open mode not authorised after migrating from 2.3

Resolution

In order to know if "open mode" is authorized on your cft 271 you can excute a cftutil listuconf (as your usual cftutil but in 271 with that new 27 command )

If you get in sysout :
D cft.secure_open_mode = No
Indeed you have to change it by executing jJCL whose model is UCNFSAMP in cft27...INSTALL library

with by exemple in CFTIN:
 //CFTIN    DD  *
  LISTUCONF scope=default,ID=cft.secure*
  UCONFSET ID=cft.secure_open_mode,value=yes
  LISTUCONF scope=default,ID=cft.secure*
 /*